Switch from GPLv2 to GPLv2+
[fw/altos] / src / drivers / ao_fat.c
index 6aae1410b8676821fec41d7d5f06bd8e6928c947..fb8eecff177322cf9b46a959f87fee4bbe9fbf89 100644 (file)
@@ -3,7 +3,8 @@
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; version 2 of the License.
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful, but
  * WITHOUT ANY WARRANTY; without even the implied warranty of
@@ -50,6 +51,9 @@ typedef ao_fat_cluster_t      cluster_t;
 typedef ao_fat_dirent_t                dirent_t;
 typedef ao_fat_cluster_offset_t        cluster_offset_t;
 
+/* Global FAT lock */
+static uint8_t ao_fat_mutex;
+
 /* Partition information, sector numbers */
 
 static uint8_t partition_type;
@@ -123,14 +127,14 @@ put_u16(uint8_t *base, uint16_t value)
 }
 
 static uint8_t
-ao_fat_cluster_valid(cluster_t cluster)
+_ao_fat_cluster_valid(cluster_t cluster)
 {
        return (2 <= cluster && cluster < number_cluster);
 }
 
 /* Start using a sector */
 static uint8_t *
-ao_fat_sector_get(sector_t sector)
+_ao_fat_sector_get(sector_t sector)
 {
        sector += partition_start;
        if (sector >= partition_end)
@@ -139,18 +143,18 @@ ao_fat_sector_get(sector_t sector)
 }
 
 /* Finish using a sector, 'w' is 1 if modified */
-#define ao_fat_sector_put(b,w) ao_bufio_put(b,w)
+#define _ao_fat_sector_put(b,w) ao_bufio_put(b,w)
 
 /* Get the next cluster entry in the chain */
 static cluster_t
-ao_fat_entry_read(cluster_t cluster)
+_ao_fat_entry_read(cluster_t cluster)
 {
        sector_t        sector;
        cluster_t       offset;
        uint8_t         *buf;
        cluster_t       ret;
 
-       if (!ao_fat_cluster_valid(cluster))
+       if (!_ao_fat_cluster_valid(cluster))
                return 0xfffffff7;
 
        if (fat32)
@@ -159,7 +163,7 @@ ao_fat_entry_read(cluster_t cluster)
                cluster <<= 1;
        sector = cluster >> (SECTOR_SHIFT);
        offset = cluster & SECTOR_MASK;
-       buf = ao_fat_sector_get(fat_start + sector);
+       buf = _ao_fat_sector_get(fat_start + sector);
        if (!buf)
                return 0;
 
@@ -171,7 +175,7 @@ ao_fat_entry_read(cluster_t cluster)
                if (AO_FAT_IS_LAST_CLUSTER16(ret))
                        ret |= 0xfff0000;
        }
-       ao_fat_sector_put(buf, 0);
+       _ao_fat_sector_put(buf, 0);
        return ret;
 }
 
@@ -179,16 +183,16 @@ ao_fat_entry_read(cluster_t cluster)
  * 'new_value'. Return the previous value.
  */
 static cluster_t
-ao_fat_entry_replace(cluster_t  cluster, cluster_t new_value)
+_ao_fat_entry_replace(cluster_t  cluster, cluster_t new_value)
 {
        sector_t                sector;
        cluster_offset_t        offset;
        uint8_t                 *buf;
-       cluster_t               ret;
+       cluster_t               ret = 0;
        cluster_t               old_value;
        uint8_t                 fat;
 
-       if (!ao_fat_cluster_valid(cluster))
+       if (!_ao_fat_cluster_valid(cluster))
                return 0xfffffff7;
 
        /* Convert from cluster index to byte index */
@@ -201,7 +205,7 @@ ao_fat_entry_replace(cluster_t  cluster, cluster_t new_value)
 
        new_value &= 0xfffffff;
        for (fat = 0; fat < number_fat; fat++) {
-               buf = ao_fat_sector_get(fat_start + fat * sectors_per_fat + sector);
+               buf = _ao_fat_sector_get(fat_start + fat * sectors_per_fat + sector);
                if (!buf)
                        return 0;
                if (fat32) {
@@ -231,7 +235,7 @@ ao_fat_entry_replace(cluster_t  cluster, cluster_t new_value)
                        }
                        put_u16(buf + offset, new_value);
                }
-               ao_fat_sector_put(buf, 1);
+               _ao_fat_sector_put(buf, 1);
        }
        return ret;
        
@@ -242,19 +246,19 @@ ao_fat_entry_replace(cluster_t  cluster, cluster_t new_value)
  * all of them as free
  */
 static void
-ao_fat_free_cluster_chain(cluster_t cluster)
+_ao_fat_free_cluster_chain(cluster_t cluster)
 {
-       while (ao_fat_cluster_valid(cluster)) {
+       while (_ao_fat_cluster_valid(cluster)) {
                if (cluster < next_free) {
                        next_free = cluster;
                        fsinfo_dirty = 1;
                }
-               cluster = ao_fat_entry_replace(cluster, 0x00000000);
+               cluster = _ao_fat_entry_replace(cluster, 0x00000000);
        }
 }
 
 /*
- * ao_fat_cluster_seek
+ * _ao_fat_cluster_seek
  * 
  * The basic file system operation -- map a file cluster index to a
  * partition cluster number. Done by computing the cluster number and
@@ -263,11 +267,11 @@ ao_fat_free_cluster_chain(cluster_t cluster)
  * is damaged somehow
  */
 static cluster_t
-ao_fat_cluster_seek(cluster_t cluster, cluster_t distance)
+_ao_fat_cluster_seek(cluster_t cluster, cluster_t distance)
 {
        while (distance) {
-               cluster = ao_fat_entry_read(cluster);
-               if (!ao_fat_cluster_valid(cluster))
+               cluster = _ao_fat_entry_read(cluster);
+               if (!_ao_fat_cluster_valid(cluster))
                        break;
                distance--;
        }
@@ -275,7 +279,7 @@ ao_fat_cluster_seek(cluster_t cluster, cluster_t distance)
 }
 
 /*
- * ao_fat_cluster_set_size
+ * _ao_fat_cluster_set_size
  *
  * Set the number of clusters in the specified chain,
  * freeing extra ones or alocating new ones as needed
@@ -284,109 +288,138 @@ ao_fat_cluster_seek(cluster_t cluster, cluster_t distance)
  */
 
 static cluster_t
-ao_fat_cluster_set_size(cluster_t first_cluster, cluster_t size)
+_ao_fat_cluster_set_size(cluster_t first_cluster, cluster_t size)
 {
-       cluster_t       clear_cluster = 0;
+       cluster_t       have;
+       cluster_t       last_cluster;
+       cluster_t       next_cluster;
+
+       /* Walk the cluster chain to the
+        * spot where it needs to change. That
+        * will either be the end of the chain (in case it needs to grow),
+        * or after the desired number of clusters, in which case it needs to shrink
+        */
+       next_cluster = first_cluster;
+       last_cluster = 0;
+       DBG("\tclusters:");
+       for (have = 0; have < size; have++) {
+               DBG(" %08x", next_cluster);
+               if (!_ao_fat_cluster_valid(next_cluster))
+                       break;
+               last_cluster = next_cluster;
+               next_cluster = _ao_fat_entry_read(next_cluster);
+       }
+       DBG("\n");
+
+       /* At this point, last_cluster points to the last valid
+        * cluster in the file, if any. That's the spot in the FAT
+        * that needs to be rewritten, either to truncate the file by
+        * writing an END marker, or to extend the file by writing
+        * more clusters. next_cluster will contain the value of the
+        * FAT at last_cluster.
+        *
+        * If this is at the head of the cluster chain, then
+        * last_cluster will be zero and next_cluster will
+        * be the first cluster in the chain.
+        */
+       if (have == size) {
+               /* The file is large enough, truncate as needed */
+               if (_ao_fat_cluster_valid(next_cluster)) {
+                       DBG("truncate between %08x and %08x\n", last_cluster, next_cluster);
+                       if (last_cluster)
+                               /*
+                                * Otherwise, rewrite the last cluster
+                                * in the chain with a LAST marker
+                                */
+                               (void) _ao_fat_entry_replace(last_cluster,
+                                                           AO_FAT_LAST_CLUSTER);
+                       else
+                               /*
+                                * If the file is getting erased, then
+                                * rewrite the directory entry cluster
+                                * value
+                                */
+                               first_cluster = 0;
 
-       if (size == 0) {
-               clear_cluster = first_cluster;
-               first_cluster = 0;
-       } else {
-               cluster_t       have;
-               cluster_t       last_cluster = 0;
-               cluster_t       next_cluster;
-
-               /* Walk the cluster chain to the
-                * spot where it needs to change. That
-                * will either be the end of the chain (in case it needs to grow),
-                * or after the desired number of clusters, in which case it needs to shrink
-                */
-               next_cluster = first_cluster;
-               for (have = 0; have < size; have++) {
-                       last_cluster = next_cluster;
-                       next_cluster = ao_fat_entry_read(last_cluster);
-                       if (!ao_fat_cluster_valid(next_cluster))
-                               break;
-               }
+                       /* Clear the remaining clusters in the chain */
+                       _ao_fat_free_cluster_chain(next_cluster);
 
-               if (have == size) {
-                       /* The file is large enough, truncate as needed */
-                       if (ao_fat_cluster_valid(next_cluster)) {
-                               /* Rewrite that cluster entry with 0xffff to mark the end of the chain */
-                               clear_cluster = ao_fat_entry_replace(last_cluster, AO_FAT_LAST_CLUSTER);
-                               filesystem_full = 0;
-                       } else {
-                               /* The chain is already the right length, don't mess with it */
-                               ;
-                       }
+                       /* The file system is no longer full (if it was) */
+                       filesystem_full = 0;
                } else {
-                       cluster_t       need;
-                       cluster_t       free;
+                       DBG("unchanged FAT chain\n");
+                       /* The chain is already the right length, don't mess with it */
+                       ;
+               }
+       } else {
+               cluster_t       need;
+               cluster_t       free;
 
-                       if (filesystem_full)
-                               return AO_FAT_BAD_CLUSTER;
+               if (filesystem_full)
+                       return AO_FAT_BAD_CLUSTER;
 
-                       if (next_free < 2 || number_cluster <= next_free) {
-                               next_free = 2;
-                               fsinfo_dirty = 1;
-                       }
+               /* Set next_free if it has wrapped or wasn't set before */
+               if (next_free < 2 || number_cluster <= next_free) {
+                       next_free = 2;
+                       fsinfo_dirty = 1;
+               }
 
-                       /* See if there are enough free clusters in the file system */
-                       need = size - have;
+               /* See if there are enough free clusters in the file system */
+               need = size - have;
 
 #define loop_cluster   for (free = next_free; need > 0;)
-#define next_cluster                                   \
-                       if (++free == number_cluster)   \
-                               free = 2;               \
-                       if (free == next_free) \
-                               break;                  \
-
-                       loop_cluster {
-                               if (!ao_fat_entry_read(free))
-                                       need--;
-                               next_cluster;
-                       }
-                       /* Still need some, tell the user that we've failed */
-                       if (need) {
-                               filesystem_full = 1;
-                               return AO_FAT_BAD_CLUSTER;
-                       }
+#define next_cluster                           \
+               if (++free == number_cluster)   \
+                       free = 2;               \
+               if (free == next_free)          \
+                       break;                  \
+
+               loop_cluster {
+                       if (!_ao_fat_entry_read(free))
+                               need--;
+                       next_cluster;
+               }
 
-                       /* Now go allocate those clusters and
-                        * thread them onto the chain
-                        */
-                       need = size - have;
-                       loop_cluster {
-                               if (!ao_fat_entry_read(free)) {
-                                       next_free = free + 1;
-                                       if (next_free >= number_cluster)
-                                               next_free = 2;
-                                       fsinfo_dirty = 1;
-                                       if (last_cluster)
-                                               ao_fat_entry_replace(last_cluster, free);
-                                       else
-                                               first_cluster = free;
-                                       last_cluster = free;
-                                       need--;
-                               }
-                               next_cluster;
+               /* Still need some, tell the user that we've failed */
+               if (need) {
+                       filesystem_full = 1;
+                       return AO_FAT_BAD_CLUSTER;
+               }
+
+               /* Now go allocate those clusters and
+                * thread them onto the chain
+                */
+               need = size - have;
+               loop_cluster {
+                       if (_ao_fat_entry_read(free) == 0) {
+                               next_free = free + 1;
+                               if (next_free >= number_cluster)
+                                       next_free = 2;
+                               fsinfo_dirty = 1;
+                               DBG("\tadd cluster. old %08x new %08x\n", last_cluster, free);
+                               if (last_cluster)
+                                       _ao_fat_entry_replace(last_cluster, free);
+                               else
+                                       first_cluster = free;
+                               last_cluster = free;
+                               need--;
                        }
+                       next_cluster;
+               }
 #undef loop_cluster
 #undef next_cluster
-                       /* Mark the new end of the chain */
-                       ao_fat_entry_replace(last_cluster, AO_FAT_LAST_CLUSTER);
-               }
+               DBG("\tlast cluster %08x\n", last_cluster);
+               /* Mark the new end of the chain */
+               _ao_fat_entry_replace(last_cluster, AO_FAT_LAST_CLUSTER);
        }
 
-       /* Deallocate clusters off the end of the file */
-       if (ao_fat_cluster_valid(clear_cluster))
-               ao_fat_free_cluster_chain(clear_cluster);
+       DBG("\tfirst cluster %08x\n", first_cluster);
        return first_cluster;
 }
 
 /* Start using a root directory entry */
 static uint8_t *
-ao_fat_root_get(dirent_t e)
+_ao_fat_root_get(dirent_t e)
 {
        offset_t                byte = e * DIRENT_SIZE;
        sector_t                sector = byte >> SECTOR_SHIFT;
@@ -396,9 +429,9 @@ ao_fat_root_get(dirent_t e)
        if (fat32) {
                cluster_t       cluster_distance = sector / sectors_per_cluster;
                sector_t        sector_index = sector % sectors_per_cluster;
-               cluster_t       cluster = ao_fat_cluster_seek(root_cluster, cluster_distance);
+               cluster_t       cluster = _ao_fat_cluster_seek(root_cluster, cluster_distance);
 
-               if (ao_fat_cluster_valid(cluster))
+               if (_ao_fat_cluster_valid(cluster))
                        sector = data_start + (cluster-2) * sectors_per_cluster + sector_index;
                else
                        return NULL;
@@ -408,7 +441,7 @@ ao_fat_root_get(dirent_t e)
                sector = root_start + sector;
        }
 
-       buf = ao_fat_sector_get(sector);
+       buf = _ao_fat_sector_get(sector);
        if (!buf)
                return NULL;
        return buf + offset;
@@ -416,41 +449,41 @@ ao_fat_root_get(dirent_t e)
 
 /* Finish using a root directory entry, 'w' is 1 if modified */
 static void
-ao_fat_root_put(uint8_t *root, dirent_t e, uint8_t write)
+_ao_fat_root_put(uint8_t *root, dirent_t e, uint8_t write)
 {
        cluster_offset_t        offset = ((e * DIRENT_SIZE) & SECTOR_MASK);
        uint8_t                 *buf = root - offset;
 
-       ao_fat_sector_put(buf, write);
+       _ao_fat_sector_put(buf, write);
 }
 
 /*
- * ao_fat_root_extend
+ * _ao_fat_root_extend
  *
  * On FAT32, make the root directory at least 'ents' entries long
  */
 static int8_t
-ao_fat_root_extend(dirent_t ents)
+_ao_fat_root_extend(dirent_t ents)
 {
        offset_t        byte_size;
        cluster_t       cluster_size;
        if (!fat32)
                return 0;
        
-       byte_size = ents * 0x20;
-       cluster_size = byte_size / bytes_per_cluster;
-       if (ao_fat_cluster_set_size(root_cluster, cluster_size) != AO_FAT_BAD_CLUSTER)
+       byte_size = (ents + 1) * 0x20;
+       cluster_size = (byte_size + bytes_per_cluster - 1) / bytes_per_cluster;
+       if (_ao_fat_cluster_set_size(root_cluster, cluster_size) != AO_FAT_BAD_CLUSTER)
                return 1;
        return 0;
 }
                
 /*
- * ao_fat_setup_partition
+ * _ao_fat_setup_partition
  * 
  * Load the boot block and find the first partition
  */
 static uint8_t
-ao_fat_setup_partition(void)
+_ao_fat_setup_partition(void)
 {
        uint8_t *mbr;
        uint8_t *partition;
@@ -509,9 +542,9 @@ ao_fat_setup_partition(void)
 }
        
 static uint8_t
-ao_fat_setup_fs(void)
+_ao_fat_setup_fs(void)
 {
-       uint8_t         *boot = ao_fat_sector_get(0);
+       uint8_t         *boot = _ao_fat_sector_get(0);
        uint32_t        data_sectors;
 
        if (!boot)
@@ -521,7 +554,7 @@ ao_fat_setup_fs(void)
        if (boot[0x1fe] != 0x55 || boot[0x1ff] != 0xaa) {
                DBG ("Invalid BOOT signature %02x %02x\n",
                        boot[0x1fe], boot[0x1ff]);
-               ao_fat_sector_put(boot, 0);
+               _ao_fat_sector_put(boot, 0);
                return AO_FAT_FILESYSTEM_INVALID_BOOT_SIGNATURE;
        }
 
@@ -529,7 +562,7 @@ ao_fat_setup_fs(void)
        if (get_u16(boot + 0xb) != SECTOR_SIZE) {
                DBG ("Invalid sector size %d\n",
                        get_u16(boot + 0xb));
-               ao_fat_sector_put(boot, 0);
+               _ao_fat_sector_put(boot, 0);
                return AO_FAT_FILESYSTEM_INVALID_SECTOR_SIZE;
        }
 
@@ -546,17 +579,17 @@ ao_fat_setup_fs(void)
                root_cluster = get_u32(boot+0x2c);
                fsinfo_sector = get_u16(boot + 0x30);
        }
-       ao_fat_sector_put(boot, 0);
+       _ao_fat_sector_put(boot, 0);
 
        free_count = 0xffffffff;
        next_free = 0;
        if (fat32 && fsinfo_sector) {
-               uint8_t *fsinfo = ao_fat_sector_get(fsinfo_sector);
+               uint8_t *fsinfo = _ao_fat_sector_get(fsinfo_sector);
 
                if (fsinfo) {
                        free_count = get_u32(fsinfo + 0x1e8);
                        next_free = get_u32(fsinfo + 0x1ec);
-                       ao_fat_sector_put(fsinfo, 0);
+                       _ao_fat_sector_put(fsinfo, 0);
                }
        }
 
@@ -572,18 +605,99 @@ ao_fat_setup_fs(void)
 }
 
 /*
- * State for the current opened file
+ * State for an open file
  */
-static struct ao_fat_dirent    ao_file_dirent;
-static uint32_t                ao_file_offset;
-static uint32_t                        ao_file_cluster_offset;
-static cluster_t               ao_file_cluster;
-static uint8_t                 ao_file_opened;
+
+struct ao_file {
+       struct ao_fat_dirent    *dirent;
+       offset_t                offset;
+       offset_t                cluster_offset;
+       cluster_t               cluster;
+       uint8_t                 busy;
+};
+
+#define AO_FAT_NFILE   8
+
+static struct ao_fat_dirent    ao_file_dirent[AO_FAT_NFILE];
+
+static struct ao_fat_dirent *
+_ao_fat_file_dirent_alloc(struct ao_fat_dirent *want)
+{
+       int8_t  d;
+       struct ao_fat_dirent *free = NULL, *dirent;
+
+       for (d = 0; d < AO_FAT_NFILE; d++) {
+
+               dirent = &ao_file_dirent[d];
+               /* See if there's another user of this file already */
+               if (want && dirent->name[0] != 0) {
+                       if (dirent->entry == want->entry)
+                               return dirent;
+               } else {
+                       if (!free) {
+                               free = dirent;
+                               if (!want)
+                                       break;
+                       }
+               }
+       }
+       if (free && want)
+               *free = *want;
+       return free;
+}
+
+static struct ao_file          ao_file_table[AO_FAT_NFILE];
+
+static int8_t
+_ao_fat_fd_alloc(struct ao_fat_dirent *dirent)
+{
+       int8_t  fd;
+
+       for (fd = 0; fd < AO_FAT_NFILE; fd++)
+               if (!ao_file_table[fd].busy) {
+                       ao_file_table[fd].dirent = _ao_fat_file_dirent_alloc(dirent);
+                       ao_file_table[fd].busy = 1;
+                       ao_file_table[fd].offset = 0;
+                       ao_file_table[fd].cluster_offset = 0;
+                       ao_file_table[fd].cluster = ao_file_table[fd].dirent->cluster;
+                               
+                       return fd;
+               }
+       return -AO_FAT_EMFILE;
+}
+
+static void
+_ao_fat_fd_free(int8_t fd)
+{
+       struct ao_file *file = &ao_file_table[fd];
+       struct ao_fat_dirent *dirent = file->dirent;
+       memset(&ao_file_table[fd], '\0', sizeof (struct ao_file));
+
+       /* Check and see if another ao_file references the same dirent */
+       for (fd = 0; fd < AO_FAT_NFILE; fd++)
+               if (ao_file_table[fd].dirent == dirent)
+                       return;
+       memset(dirent, '\0', sizeof (struct ao_fat_dirent));
+}
+
+static struct ao_file *
+_ao_fat_fd_to_file(int8_t fd)
+{
+       struct ao_file *file;
+       if (fd < 0 || AO_FAT_NFILE <= fd)
+               return NULL;
+
+       file = &ao_file_table[fd];
+       if (!file->busy)
+               return NULL;
+       return file;
+}
+
 static uint8_t                 ao_filesystem_setup;
 static uint8_t                 ao_filesystem_status;
 
 static uint8_t
-ao_fat_setup(void)
+_ao_fat_setup(void)
 {
        if (!ao_filesystem_setup) {
 
@@ -599,13 +713,14 @@ ao_fat_setup(void)
                number_cluster = fat_start = root_start = data_start = 0;
                next_free = filesystem_full = 0;
                fat32 = fsinfo_dirty = root_cluster = fsinfo_sector = free_count = 0;
-               memset(&ao_file_dirent, '\0', sizeof (ao_file_dirent));
 
-               ao_file_offset = ao_file_cluster_offset = ao_file_cluster = ao_file_opened = 0;
-               ao_filesystem_status = ao_fat_setup_partition();
+               /* Reset open file table */
+               memset(&ao_file_table, '\0', sizeof (ao_file_table));
+
+               ao_filesystem_status = _ao_fat_setup_partition();
                if (ao_filesystem_status != AO_FAT_FILESYSTEM_SUCCESS)
                        return ao_filesystem_status;
-               ao_filesystem_status = ao_fat_setup_fs();
+               ao_filesystem_status = _ao_fat_setup_fs();
                if (ao_filesystem_status != AO_FAT_FILESYSTEM_SUCCESS)
                        return ao_filesystem_status;
        }
@@ -623,7 +738,7 @@ ao_fat_unmount(void)
  */
 
 static uint32_t
-ao_fat_current_sector(void)
+_ao_fat_current_sector(struct ao_file *file)
 {
        cluster_t       cluster_offset;
        uint32_t        sector_offset;
@@ -631,87 +746,114 @@ ao_fat_current_sector(void)
        cluster_t       cluster;
 
        DBG("current sector offset %d size %d\n",
-           ao_file_offset, ao_file_dirent.size);
+           file->offset, file->dirent->size);
 
-       if (ao_file_offset > ao_file_dirent.size)
+       if (file->offset > (offset_t) file->dirent->size) {
+               printf ("file offset %d larger than size %d\n",
+                       file->offset, file->dirent->size);
                return 0xffffffff;
+       }
 
-       sector_offset = ao_file_offset >> SECTOR_SHIFT;
+       sector_offset = file->offset >> SECTOR_SHIFT;
 
-       if (!ao_file_cluster || ao_file_offset < ao_file_cluster_offset) {
-               ao_file_cluster = ao_file_dirent.cluster;
-               ao_file_cluster_offset = 0;
-               DBG("\treset to start of file %08x\n", ao_file_cluster);
+       if (!file->cluster || file->offset < file->cluster_offset) {
+               file->cluster = file->dirent->cluster;
+               file->cluster_offset = 0;
+               DBG("\treset to start of file %08x\n", file->cluster);
        }
 
-       if (ao_file_cluster_offset + bytes_per_cluster <= ao_file_offset) {
+       if ((offset_t) (file->cluster_offset + bytes_per_cluster) <= file->offset) {
                cluster_t       cluster_distance;
 
                cluster_offset = sector_offset / sectors_per_cluster;
 
-               cluster_distance = cluster_offset - ao_file_cluster_offset / bytes_per_cluster;
+               cluster_distance = cluster_offset - file->cluster_offset / bytes_per_cluster;
 
                DBG("\tseek forward %d clusters\n", cluster_distance);
-               cluster = ao_fat_cluster_seek(ao_file_cluster, cluster_distance);
+               cluster = _ao_fat_cluster_seek(file->cluster, cluster_distance);
 
-               if (!ao_fat_cluster_valid(cluster))
+               if (!_ao_fat_cluster_valid(cluster)) {
+                       printf ("invalid cluster %08x\n", cluster);
                        return 0xffffffff;
-               ao_file_cluster = cluster;
-               ao_file_cluster_offset = cluster_offset * bytes_per_cluster;
+               }
+               file->cluster = cluster;
+               file->cluster_offset = cluster_offset * bytes_per_cluster;
        }
 
        sector_index = sector_offset % sectors_per_cluster;
        DBG("current cluster %08x sector_index %d sector %d\n",
-           ao_file_cluster, sector_index,
-           data_start + (uint32_t) (ao_file_cluster-2) * sectors_per_cluster + sector_index);
-       return data_start + (uint32_t) (ao_file_cluster-2) * sectors_per_cluster + sector_index;
+           file->cluster, sector_index,
+           data_start + (uint32_t) (file->cluster-2) * sectors_per_cluster + sector_index);
+       return data_start + (uint32_t) (file->cluster-2) * sectors_per_cluster + sector_index;
 }
 
+/*
+ * _ao_fat_invaldate_cluster_offset
+ *
+ * When the file size gets shrunk, invalidate
+ * any file structures referencing clusters beyond that point
+ */
+
 static void
-ao_fat_set_offset(uint32_t offset)
+_ao_fat_invalidate_cluster_offset(struct ao_fat_dirent *dirent)
 {
-       DBG("Set offset %d\n", offset);
-       ao_file_offset = offset;
+       int8_t          fd;
+       struct ao_file  *file;
+
+       for (fd = 0; fd < AO_FAT_NFILE; fd++) {
+               file = &ao_file_table[fd];
+               if (!file->busy)
+                       continue;
+               if (file->dirent == dirent) {
+                       if (file->cluster_offset >= (offset_t) dirent->size) {
+                               file->cluster_offset = 0;
+                               file->cluster = dirent->cluster;
+                       }
+               }
+       }
 }
 
 /*
- * ao_fat_set_size
+ * _ao_fat_set_size
  *
  * Set the size of the current file, truncating or extending
  * the cluster chain as needed
  */
 static int8_t
-ao_fat_set_size(uint32_t size)
+_ao_fat_set_size(struct ao_file *file, uint32_t size)
 {
        uint8_t         *dent;
        cluster_t       first_cluster;
        cluster_t       have_clusters, need_clusters;
 
        DBG ("Set size %d\n", size);
-       if (size == ao_file_dirent.size) {
+       if (size == file->dirent->size) {
                DBG("\tsize match\n");
                return AO_FAT_SUCCESS;
        }
 
-       first_cluster = ao_file_dirent.cluster;
-       have_clusters = (ao_file_dirent.size + bytes_per_cluster - 1) / bytes_per_cluster;
+       first_cluster = file->dirent->cluster;
+       have_clusters = (file->dirent->size + bytes_per_cluster - 1) / bytes_per_cluster;
        need_clusters = (size + bytes_per_cluster - 1) / bytes_per_cluster;
 
        DBG ("\tfirst cluster %08x have %d need %d\n", first_cluster, have_clusters, need_clusters);
        if (have_clusters != need_clusters) {
-               if (ao_file_cluster && size >= ao_file_cluster_offset) {
-                       cluster_t       offset_clusters = (ao_file_cluster_offset + bytes_per_cluster) / bytes_per_cluster;
+               if (file->cluster && (offset_t) size > file->cluster_offset) {
+                       cluster_t       offset_clusters = (file->cluster_offset + bytes_per_cluster) / bytes_per_cluster;
                        cluster_t       extra_clusters = need_clusters - offset_clusters;
                        cluster_t       next_cluster;
 
                        DBG ("\tset size relative offset_clusters %d extra_clusters %d\n",
                             offset_clusters, extra_clusters);
-                       next_cluster = ao_fat_cluster_set_size(ao_file_cluster, extra_clusters);
+
+                       /* Need one more to account for file->cluster, which we already have */
+                       next_cluster = _ao_fat_cluster_set_size(file->cluster, extra_clusters + 1);
                        if (next_cluster == AO_FAT_BAD_CLUSTER)
                                return -AO_FAT_ENOSPC;
                } else {
                        DBG ("\tset size absolute need_clusters %d\n", need_clusters);
-                       first_cluster = ao_fat_cluster_set_size(first_cluster, need_clusters);
+                       first_cluster = _ao_fat_cluster_set_size(first_cluster, need_clusters);
 
                        if (first_cluster == AO_FAT_BAD_CLUSTER)
                                return -AO_FAT_ENOSPC;
@@ -720,29 +862,34 @@ ao_fat_set_size(uint32_t size)
 
        DBG ("\tupdate directory size\n");
        /* Update the directory entry */
-       dent = ao_fat_root_get(ao_file_dirent.entry);
-       if (!dent)
+       dent = _ao_fat_root_get(file->dirent->entry);
+       if (!dent) {
+               printf ("dent update failed\n");
                return -AO_FAT_EIO;
+       }
        put_u32(dent + 0x1c, size);
        put_u16(dent + 0x1a, first_cluster);
        if (fat32)
                put_u16(dent + 0x14, first_cluster >> 16);
-       ao_fat_root_put(dent, ao_file_dirent.entry, 1);
+       _ao_fat_root_put(dent, file->dirent->entry, 1);
 
-       ao_file_dirent.size = size;
-       ao_file_dirent.cluster = first_cluster;
+       file->dirent->size = size;
+       file->dirent->cluster = first_cluster;
+       if (have_clusters > need_clusters)
+               _ao_fat_invalidate_cluster_offset(file->dirent);
        DBG ("set size done\n");
        return AO_FAT_SUCCESS;
 }
 
 /*
- * ao_fat_root_init
+ * _ao_fat_root_init
  *
  * Initialize a root directory entry
  */
 static void
-ao_fat_root_init(uint8_t *dent, char name[11], uint8_t attr)
+_ao_fat_root_init(uint8_t *dent, char name[11], uint8_t attr)
 {
+       (void) attr;
        memset(dent, '\0', 0x20);
        memmove(dent, name, 11);
 
@@ -774,7 +921,7 @@ ao_fat_root_init(uint8_t *dent, char name[11], uint8_t attr)
 
 
 static void
-ao_fat_dirent_init(uint8_t *dent, uint16_t entry, struct ao_fat_dirent *dirent)
+_ao_fat_dirent_init(struct ao_fat_dirent *dirent, uint8_t *dent, uint16_t entry)
 {
        memcpy(dirent->name, dent + 0x00, 11);
        dirent->attr = dent[0x0b];
@@ -786,13 +933,13 @@ ao_fat_dirent_init(uint8_t *dent, uint16_t entry, struct ao_fat_dirent *dirent)
 }
 
 /*
- * ao_fat_flush_fsinfo
+ * _ao_fat_flush_fsinfo
  *
  * Write out any fsinfo changes to disk
  */
 
 static void
-ao_fat_flush_fsinfo(void)
+_ao_fat_flush_fsinfo(void)
 {
        uint8_t *fsinfo;
 
@@ -805,11 +952,11 @@ ao_fat_flush_fsinfo(void)
        if (!fsinfo_sector)
                return;
 
-       fsinfo = ao_fat_sector_get(fsinfo_sector);
+       fsinfo = _ao_fat_sector_get(fsinfo_sector);
        if (fsinfo) {
                put_u32(fsinfo + 0x1e8, free_count);
                put_u32(fsinfo + 0x1ec, next_free);
-               ao_fat_sector_put(fsinfo, 1);
+               _ao_fat_sector_put(fsinfo, 1);
        }
 }
 
@@ -823,15 +970,23 @@ ao_fat_flush_fsinfo(void)
  * Flush any pending I/O to storage
  */
 
-void
-ao_fat_sync(void)
+static void
+_ao_fat_sync(void)
 {
-       if (ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
+       if (_ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
                return;
-       ao_fat_flush_fsinfo();
+       _ao_fat_flush_fsinfo();
        ao_bufio_flush();
 }
 
+void
+ao_fat_sync(void)
+{
+       ao_mutex_get(&ao_fat_mutex);
+       _ao_fat_sync();
+       ao_mutex_put(&ao_fat_mutex);
+}
+
 /*
  * ao_fat_full
  *
@@ -842,29 +997,76 @@ ao_fat_sync(void)
 int8_t
 ao_fat_full(void)
 {
-       if (ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
+       ao_mutex_get(&ao_fat_mutex);
+       if (_ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS) {
+               ao_mutex_put(&ao_fat_mutex);
                return 1;
+       }
+       ao_mutex_put(&ao_fat_mutex);
        return filesystem_full;
 }
 
+static int8_t
+_ao_fat_readdir(uint16_t *entry, struct ao_fat_dirent *dirent)
+{
+       uint8_t *dent;
+
+       if (_ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
+               return -AO_FAT_EIO;
+
+       for (;;) {
+               dent = _ao_fat_root_get(*entry);
+               if (!dent)
+                       return -AO_FAT_EDIREOF;
+
+               if (dent[0] == AO_FAT_DENT_END) {
+                       _ao_fat_root_put(dent, *entry, 0);
+                       return -AO_FAT_EDIREOF;
+               }
+               if (dent[0] != AO_FAT_DENT_EMPTY && (dent[0xb] & 0xf) != 0xf) {
+                       _ao_fat_dirent_init(dirent, dent, *entry);
+                       _ao_fat_root_put(dent, *entry, 0);
+                       (*entry)++;
+                       return AO_FAT_SUCCESS;
+               }
+               _ao_fat_root_put(dent, *entry, 0);
+               (*entry)++;
+       }
+}
+
+int8_t
+ao_fat_readdir(uint16_t *entry, struct ao_fat_dirent *dirent)
+{
+       int8_t status;
+
+       ao_mutex_get(&ao_fat_mutex);
+       status = _ao_fat_readdir(entry, dirent);
+       ao_mutex_put(&ao_fat_mutex);
+       return status;
+}
+
 /*
  * ao_fat_open
  *
  * Open an existing file.
  */
-int8_t
-ao_fat_open(char name[11], uint8_t mode)
+static int8_t
+_ao_fat_open(char name[11], uint8_t mode)
 {
        uint16_t                entry = 0;
-       struct ao_fat_dirent    dirent;
+       static struct ao_fat_dirent     dirent;
+       int8_t                  status;
 
-       if (ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
+       if (_ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
                return -AO_FAT_EIO;
 
-       if (ao_file_opened)
-               return -AO_FAT_EMFILE;
-       
-       while (ao_fat_readdir(&entry, &dirent)) {
+       for (;;) {
+               status = _ao_fat_readdir(&entry, &dirent);
+               if (status < 0) {
+                       if (status == -AO_FAT_EDIREOF)
+                               return -AO_FAT_ENOENT;
+                       return status;
+               }
                if (!memcmp(name, dirent.name, 11)) {
                        if (AO_FAT_IS_DIR(dirent.attr))
                                return -AO_FAT_EISDIR;
@@ -872,87 +1074,130 @@ ao_fat_open(char name[11], uint8_t mode)
                                return -AO_FAT_EPERM;
                        if (mode > AO_FAT_OPEN_READ && (dirent.attr & AO_FAT_FILE_READ_ONLY))
                                return -AO_FAT_EACCESS;
-                       ao_file_dirent = dirent;
-                       ao_fat_set_offset(0);
-                       ao_file_opened = 1;
-                       return AO_FAT_SUCCESS;
+                       return _ao_fat_fd_alloc(&dirent);
                }
        }
        return -AO_FAT_ENOENT;
 }
 
+int8_t
+ao_fat_open(char name[11], uint8_t mode)
+{
+       int8_t status;
+
+       ao_mutex_get(&ao_fat_mutex);
+       status = _ao_fat_open(name, mode);
+       ao_mutex_put(&ao_fat_mutex);
+       return status;
+}
+
+/*
+ * ao_fat_close
+ *
+ * Close the currently open file
+ */
+static int8_t
+_ao_fat_close(int8_t fd)
+{
+       struct ao_file *file;
+
+       file = _ao_fat_fd_to_file(fd);
+       if (!file)
+               return -AO_FAT_EBADF;
+
+       _ao_fat_fd_free(fd);
+       _ao_fat_sync();
+       return AO_FAT_SUCCESS;
+}
+
+int8_t
+ao_fat_close(int8_t fd)
+{
+       int8_t status;
+
+       ao_mutex_get(&ao_fat_mutex);
+       status = _ao_fat_close(fd);
+       ao_mutex_put(&ao_fat_mutex);
+       return status;
+}
+
 /*
  * ao_fat_creat
  *
  * Open and truncate an existing file or
  * create a new file
  */
-int8_t
-ao_fat_creat(char name[11])
+
+static int8_t
+_ao_fat_creat(char name[11])
 {
-       uint16_t        entry;
-       int8_t          status;
-       uint8_t         *dent;
+       uint16_t                entry;
+       int8_t                  fd;
+       int8_t                  status;
+       uint8_t                 *dent;
+       struct ao_file          *file;
 
-       if (ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
+       if (_ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
                return -AO_FAT_EIO;
 
-       if (ao_file_opened)
-               return -AO_FAT_EMFILE;
+       fd = _ao_fat_open(name, AO_FAT_OPEN_WRITE);
+       if (fd >= 0) {
+               file = &ao_file_table[fd];
+               status = _ao_fat_set_size(file, 0);
+               if (status < 0) {
+                       _ao_fat_close(fd);
+                       fd = status;
+               }
+       } else {
+               if (fd == -AO_FAT_ENOENT) {
+                       entry = 0;
+                       for (;;) {
+                               dent = _ao_fat_root_get(entry);
+                               if (!dent) {
+                               
+                                       if (_ao_fat_root_extend(entry))
+                                               continue;
+                                       fd = -AO_FAT_ENOSPC;
+                                       break;
+                               }
+                               if (dent[0] == AO_FAT_DENT_EMPTY || dent[0] == AO_FAT_DENT_END) {
+                                       fd = _ao_fat_fd_alloc(NULL);
+                                       if (fd < 0) {
+                                               _ao_fat_root_put(dent, entry, 0);
+                                               break;
+                                       }
 
-       status = ao_fat_open(name, AO_FAT_OPEN_WRITE);
+                                       file = &ao_file_table[fd];
+                                       /* Initialize the dent */
+                                       _ao_fat_root_init(dent, name, AO_FAT_FILE_REGULAR);
 
-       switch (status) {
-       case -AO_FAT_SUCCESS:
-               status = ao_fat_set_size(0);
-               break;
-       case -AO_FAT_ENOENT:
-               entry = 0;
-               for (;;) {
-                       dent = ao_fat_root_get(entry);
-                       if (!dent) {
-                               
-                               if (ao_fat_root_extend(entry))
-                                       continue;
-                               status = -AO_FAT_ENOSPC;
-                               break;
-                       }
-                               
-                       if (dent[0] == AO_FAT_DENT_EMPTY || dent[0] == AO_FAT_DENT_END) {
-                               ao_fat_root_init(dent, name, AO_FAT_FILE_REGULAR);
-                               ao_fat_dirent_init(dent, entry,  &ao_file_dirent);
-                               ao_fat_root_put(dent, entry, 1);
-                               ao_file_opened = 1;
-                               ao_fat_set_offset(0);
-                               status = -AO_FAT_SUCCESS;
-                               break;
-                       } else {
-                               ao_fat_root_put(dent, entry, 0);
+                                       /* Now initialize the dirent from the dent */
+                                       _ao_fat_dirent_init(file->dirent, dent, entry);
+
+                                       /* And write the dent to storage */
+                                       _ao_fat_root_put(dent, entry, 1);
+
+                                       status = -AO_FAT_SUCCESS;
+                                       break;
+                               } else {
+                                       _ao_fat_root_put(dent, entry, 0);
+                               }
+                               entry++;
                        }
-                       entry++;
                }
        }
-       return status;
+       return fd;
 }
 
-/*
- * ao_fat_close
- *
- * Close the currently open file
- */
 int8_t
-ao_fat_close(void)
+ao_fat_creat(char name[11])
 {
-       if (!ao_file_opened)
-               return -AO_FAT_EBADF;
+       int8_t  status;
 
-       memset(&ao_file_dirent, '\0', sizeof (struct ao_fat_dirent));
-       ao_file_offset = 0;
-       ao_file_cluster = 0;
-       ao_file_opened = 0;
-
-       ao_fat_sync();
-       return AO_FAT_SUCCESS;
+       ao_mutex_get(&ao_fat_mutex);
+       status = _ao_fat_creat(name);
+       ao_mutex_put(&ao_fat_mutex);
+       return status;
 }
 
 /*
@@ -962,17 +1207,20 @@ ao_fat_close(void)
  */
 
 static void *
-ao_fat_map_current(int len, cluster_offset_t *offsetp, cluster_offset_t *this_time)
+ao_fat_map_current(struct ao_file *file, int len, cluster_offset_t *offsetp, cluster_offset_t *this_time)
 {
        cluster_offset_t        offset;
        sector_t                sector;
        void                    *buf;
 
-       offset = ao_file_offset & SECTOR_MASK;
-       sector = ao_fat_current_sector();
-       if (sector == 0xffffffff)
+       offset = file->offset & SECTOR_MASK;
+       sector = _ao_fat_current_sector(file);
+       if (sector == 0xffffffff) {
+               return NULL;
+       }
+       buf = _ao_fat_sector_get(sector);
+       if (!buf)
                return NULL;
-       buf = ao_fat_sector_get(sector);
        if (offset + len < SECTOR_SIZE)
                *this_time = len;
        else
@@ -987,37 +1235,44 @@ ao_fat_map_current(int len, cluster_offset_t *offsetp, cluster_offset_t *this_ti
  * Read from the file
  */
 int
-ao_fat_read(void *dst, int len)
+ao_fat_read(int8_t fd, void *dst, int len)
 {
        uint8_t                 *dst_b = dst;
        cluster_offset_t        this_time;
        cluster_offset_t        offset;
        uint8_t                 *buf;
        int                     ret = 0;
+       struct ao_file          *file;
 
-       if (!ao_file_opened)
-               return -AO_FAT_EBADF;
+       ao_mutex_get(&ao_fat_mutex);
+       file = _ao_fat_fd_to_file(fd);
+       if (!file) {
+               ret = -AO_FAT_EBADF;
+               goto done;
+       }
 
-       if (ao_file_offset + len > ao_file_dirent.size)
-               len = ao_file_dirent.size - ao_file_offset;
+       if (file->offset + len > (offset_t) file->dirent->size)
+               len = file->dirent->size - file->offset;
 
        if (len < 0)
                len = 0;
 
        while (len) {
-               buf = ao_fat_map_current(len, &offset, &this_time);
+               buf = ao_fat_map_current(file, len, &offset, &this_time);
                if (!buf) {
                        ret = -AO_FAT_EIO;
                        break;
                }
                memcpy(dst_b, buf + offset, this_time);
-               ao_fat_sector_put(buf, 0);
+               _ao_fat_sector_put(buf, 0);
 
                ret += this_time;
                len -= this_time;
                dst_b += this_time;
-               ao_fat_set_offset(ao_file_offset + this_time);
+               file->offset = file->offset + this_time;
        }
+done:
+       ao_mutex_put(&ao_fat_mutex);
        return ret;
 }
 
@@ -1027,37 +1282,44 @@ ao_fat_read(void *dst, int len)
  * Write to the file, extended as necessary
  */
 int
-ao_fat_write(void *src, int len)
+ao_fat_write(int8_t fd, void *src, int len)
 {
-       uint8_t         *src_b = src;
-       uint16_t        this_time;
-       uint16_t        offset;
-       uint8_t         *buf;
-       int             ret = 0;
+       uint8_t                 *src_b = src;
+       cluster_offset_t        this_time;
+       cluster_offset_t        offset;
+       uint8_t                 *buf;
+       int                     ret = 0;
+       struct ao_file          *file;
 
-       if (!ao_file_opened)
-               return -AO_FAT_EBADF;
+       ao_mutex_get(&ao_fat_mutex);
+       file = _ao_fat_fd_to_file(fd);
+       if (!file) {
+               ret = -AO_FAT_EBADF;
+               goto done;
+       }
 
-       if (ao_file_offset + len > ao_file_dirent.size) {
-               ret = ao_fat_set_size(ao_file_offset + len);
+       if (file->offset + len > (offset_t) file->dirent->size) {
+               ret = _ao_fat_set_size(file, file->offset + len);
                if (ret < 0)
-                       return ret;
+                       goto done;
        }
 
        while (len) {
-               buf = ao_fat_map_current(len, &offset, &this_time);
+               buf = ao_fat_map_current(file, len, &offset, &this_time);
                if (!buf) {
                        ret = -AO_FAT_EIO;
                        break;
                }
                memcpy(buf + offset, src_b, this_time);
-               ao_fat_sector_put(buf, 1);
+               _ao_fat_sector_put(buf, 1);
 
                ret += this_time;
                len -= this_time;
                src_b += this_time;
-               ao_fat_set_offset(ao_file_offset + this_time);
+               file->offset = file->offset + this_time;
        }
+done:
+       ao_mutex_put(&ao_fat_mutex);
        return ret;
 }
 
@@ -1071,13 +1333,20 @@ ao_fat_write(void *src, int len)
  * write
  */
 int32_t
-ao_fat_seek(int32_t pos, uint8_t whence)
+ao_fat_seek(int8_t fd, int32_t pos, uint8_t whence)
 {
-       uint32_t        new_offset = ao_file_offset;
-
-       if (!ao_file_opened)
-               return -AO_FAT_EBADF;
+       offset_t        new_offset;
+       struct ao_file  *file;
+       int32_t         ret;
+
+       ao_mutex_get(&ao_fat_mutex);
+       file = _ao_fat_fd_to_file(fd);
+       if (!file) {
+               ret = -AO_FAT_EBADF;
+               goto done;
+       }
 
+       new_offset = file->offset;
        switch (whence) {
        case AO_FAT_SEEK_SET:
                new_offset = pos;
@@ -1086,11 +1355,13 @@ ao_fat_seek(int32_t pos, uint8_t whence)
                new_offset += pos;
                break;
        case AO_FAT_SEEK_END:
-               new_offset = ao_file_dirent.size + pos;
+               new_offset = file->dirent->size + pos;
                break;
        }
-       ao_fat_set_offset(new_offset);
-       return ao_file_offset;
+       ret = file->offset = new_offset;
+done:
+       ao_mutex_put(&ao_fat_mutex);
+       return ret;
 }
 
 /*
@@ -1103,10 +1374,14 @@ int8_t
 ao_fat_unlink(char name[11])
 {
        uint16_t                entry = 0;
-       struct ao_fat_dirent    dirent;
+       static struct ao_fat_dirent     dirent;
+       int8_t                  ret;
 
-       if (ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
-               return -AO_FAT_EIO;
+       ao_mutex_get(&ao_fat_mutex);
+       if (_ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS) {
+               ret = -AO_FAT_EIO;
+               goto done;
+       }
 
        while (ao_fat_readdir(&entry, &dirent)) {
                if (memcmp(name, dirent.name, 11) == 0) {
@@ -1114,66 +1389,48 @@ ao_fat_unlink(char name[11])
                        uint8_t *ent;
                        uint8_t delete;
 
-                       if (AO_FAT_IS_DIR(dirent.attr))
-                               return -AO_FAT_EISDIR;
-                       if (!AO_FAT_IS_FILE(dirent.attr))
-                               return -AO_FAT_EPERM;
+                       if (AO_FAT_IS_DIR(dirent.attr)) {
+                               ret = -AO_FAT_EISDIR;
+                               goto done;
+                       }
+                       if (!AO_FAT_IS_FILE(dirent.attr)) {
+                               ret = -AO_FAT_EPERM;
+                               goto done;
+                       }
 
-                       ao_fat_free_cluster_chain(dirent.cluster);
-                       next = ao_fat_root_get(dirent.entry + 1);
+                       _ao_fat_free_cluster_chain(dirent.cluster);
+                       next = _ao_fat_root_get(dirent.entry + 1);
                        if (next && next[0] != AO_FAT_DENT_END)
                                delete = AO_FAT_DENT_EMPTY;
                        else
                                delete = AO_FAT_DENT_END;
                        if (next)
-                               ao_fat_root_put(next, dirent.entry + 1, 0);
-                       ent = ao_fat_root_get(dirent.entry);
+                               _ao_fat_root_put(next, dirent.entry + 1, 0);
+                       ent = _ao_fat_root_get(dirent.entry);
                        if (ent) {
                                memset(ent, '\0', DIRENT_SIZE);
                                *ent = delete;
-                               ao_fat_root_put(ent, dirent.entry, 1);
+                               _ao_fat_root_put(ent, dirent.entry, 1);
                        }
                        ao_bufio_flush();
-                       return AO_FAT_SUCCESS;
+                       ret = AO_FAT_SUCCESS;
+                       goto done;
                }
        }
-       return -AO_FAT_ENOENT;
+       ret = -AO_FAT_ENOENT;
+done:
+       ao_mutex_put(&ao_fat_mutex);
+       return ret;
 }
 
 int8_t
 ao_fat_rename(char old[11], char new[11])
 {
+       (void) old;
+       (void) new;
        return -AO_FAT_EIO;
 }
 
-int8_t
-ao_fat_readdir(uint16_t *entry, struct ao_fat_dirent *dirent)
-{
-       uint8_t *dent;
-
-       if (ao_fat_setup() != AO_FAT_FILESYSTEM_SUCCESS)
-               return -AO_FAT_EIO;
-
-       for (;;) {
-               dent = ao_fat_root_get(*entry);
-               if (!dent)
-                       return -AO_FAT_EDIREOF;
-
-               if (dent[0] == AO_FAT_DENT_END) {
-                       ao_fat_root_put(dent, *entry, 0);
-                       return -AO_FAT_EDIREOF;
-               }
-               if (dent[0] != AO_FAT_DENT_EMPTY && (dent[0xb] & 0xf) != 0xf) {
-                       ao_fat_dirent_init(dent, *entry, dirent);
-                       ao_fat_root_put(dent, *entry, 0);
-                       (*entry)++;
-                       return AO_FAT_SUCCESS;
-               }
-               ao_fat_root_put(dent, *entry, 0);
-               (*entry)++;
-       }
-}
-
 #if FAT_COMMANDS
 
 static const char *filesystem_errors[] = {
@@ -1192,7 +1449,8 @@ ao_fat_mbr_cmd(void)
 {
        uint8_t status;
 
-       status = ao_fat_setup();
+       ao_mutex_get(&ao_fat_mutex);
+       status = _ao_fat_setup();
        if (status == AO_FAT_FILESYSTEM_SUCCESS) {
                printf ("partition type: %02x\n", partition_type);
                printf ("partition start: %08x\n", partition_start);
@@ -1212,6 +1470,7 @@ ao_fat_mbr_cmd(void)
        } else {
                printf ("FAT filesystem not available: %s\n", filesystem_errors[status]);
        }
+       ao_mutex_put(&ao_fat_mutex);
 }
 
 struct ao_fat_attr {
@@ -1234,7 +1493,7 @@ static void
 ao_fat_list_cmd(void)
 {
        uint16_t                entry = 0;
-       struct ao_fat_dirent    dirent;
+       static struct ao_fat_dirent     dirent;
        int                     i;
        int8_t                  status;
 
@@ -1244,7 +1503,7 @@ ao_fat_list_cmd(void)
                putchar('.');
                for (; i < 11; i++)
                        putchar(dirent.name[i]);
-               for (i = 0; i < NUM_FAT_ATTR; i++)
+               for (i = 0; i < (int) NUM_FAT_ATTR; i++)
                        putchar (dirent.attr & ao_fat_attr[i].bit ? ao_fat_attr[i].label : ' ');
                printf (" @%08x %d\n", dirent.cluster, dirent.size);
        }
@@ -1252,7 +1511,7 @@ ao_fat_list_cmd(void)
                printf ("readdir failed: %d\n", status);
 }
 
-static uint8_t
+static void
 ao_fat_parse_name(char name[11])
 {
        uint8_t c;
@@ -1275,12 +1534,12 @@ ao_fat_parse_name(char name[11])
 }
 
 static void
-ao_fat_show_cmd(void)
+ao_fat_dump_cmd(void)
 {
-       char            name[11];
-       int8_t          status;
+       static char     name[11];
+       int8_t          fd;
        int             cnt, i;
-       char            buf[64];
+       static char     buf[32];
 
        ao_fat_parse_name(name);
        if (name[0] == '\0') {
@@ -1288,31 +1547,25 @@ ao_fat_show_cmd(void)
                return;
        }
                
-       status = ao_fat_open(name, AO_FAT_OPEN_READ);
-       if (status) {
-               printf ("Open failed: %d\n", status);
+       fd = ao_fat_open(name, AO_FAT_OPEN_READ);
+       if (fd < 0) {
+               printf ("Open failed: %d\n", fd);
                return;
        }
-       while ((cnt = ao_fat_read(buf, sizeof(buf))) > 0) {
+       while ((cnt = ao_fat_read(fd, buf, sizeof(buf))) > 0) {
                for (i = 0; i < cnt; i++)
                        putchar(buf[i]);
        }
-       ao_fat_close();
-}
-
-static void
-ao_fat_putchar(char c)
-{
+       ao_fat_close(fd);
 }
 
 static void
 ao_fat_write_cmd(void)
 {
-       char            name[11];
-       int8_t          status;
-       int             cnt, i;
-       char            buf[64];
+       static char     name[11];
+       int8_t          fd;
        char            c;
+       int             status;
 
        ao_fat_parse_name(name);
        if (name[0] == '\0') {
@@ -1320,9 +1573,9 @@ ao_fat_write_cmd(void)
                return;
        }
                
-       status = ao_fat_creat(name);
-       if (status) {
-               printf ("Open failed: %d\n", status);
+       fd = ao_fat_creat(name);
+       if (fd < 0) {
+               printf ("Open failed: %d\n", fd);
                return;
        }
        flush();
@@ -1332,19 +1585,61 @@ ao_fat_write_cmd(void)
                        if (c == '\n') putchar ('\r');
                        putchar(c); flush();
                }
-               if (ao_fat_write(&c, 1) != 1) {
-                       printf ("Write failure\n");
+               status = ao_fat_write(fd, &c, 1);
+               if (status != 1) {
+                       printf ("Write failure %d\n", status);
                        break;
                }
        }
-       ao_fat_close();
+       ao_fat_close(fd);
+}
+
+static void
+put32(uint32_t a)
+{
+       ao_cmd_put16(a >> 16);
+       ao_cmd_put16(a);
+}
+
+static void
+ao_fat_hexdump_cmd(void)
+{
+       char            name[11];
+       int8_t          fd;
+       int             cnt, i;
+       char            buf[8];
+       uint32_t        addr;
+
+       ao_fat_parse_name(name);
+       if (name[0] == '\0') {
+               ao_cmd_status = ao_cmd_syntax_error;
+               return;
+       }
+               
+       fd = ao_fat_open(name, AO_FAT_OPEN_READ);
+       if (fd < 0) {
+               printf ("Open failed: %d\n", fd);
+               return;
+       }
+       addr = 0;
+       while ((cnt = ao_fat_read(fd, buf, sizeof(buf))) > 0) {
+               put32(addr);
+               for (i = 0; i < cnt; i++) {
+                       putchar(' ');
+                       ao_cmd_put8(buf[i]);
+               }
+               putchar('\n');
+               addr += cnt;
+       }
+       ao_fat_close(fd);
 }
 
 static const struct ao_cmds ao_fat_cmds[] = {
        { ao_fat_mbr_cmd,       "M\0Show FAT MBR and other info" },
        { ao_fat_list_cmd,      "F\0List FAT directory" },
-       { ao_fat_show_cmd,      "S <name>\0Show FAT file" },
+       { ao_fat_dump_cmd,      "D <name>\0Dump FAT file" },
        { ao_fat_write_cmd,     "W <name>\0Write FAT file (end with ^D)" },
+       { ao_fat_hexdump_cmd,   "H <name>\0HEX dump FAT file" },
        { 0, NULL },
 };