X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=blobdiff_plain;f=src%2Fdrivers%2Fao_fat.c;h=fb8eecff177322cf9b46a959f87fee4bbe9fbf89;hp=9cd3d34be25b32cc83ccae414befd1e1b1b5a204;hb=1085ec5d57e0ed5d132f2bbdac1a0b6a32c0ab4a;hpb=144b44e13ce3361ff59cbb555e84d542455a4e17

diff --git a/src/drivers/ao_fat.c b/src/drivers/ao_fat.c
index 9cd3d34b..fb8eecff 100644
--- a/src/drivers/ao_fat.c
+++ b/src/drivers/ao_fat.c
@@ -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
@@ -30,6 +31,10 @@
 /* Spew FAT tracing */
 #define FAT_TRACE	0
  
+#ifdef DBG
+#undef DBG
+#endif
+
 #if FAT_TRACE
 #define DBG(...) printf(__VA_ARGS__)
 #else
@@ -46,6 +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;
@@ -119,14 +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)
@@ -135,18 +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)
@@ -155,7 +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;
 
@@ -167,7 +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;
 }
 
@@ -175,16 +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 */
@@ -197,7 +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) {
@@ -227,7 +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;
 	
@@ -238,19 +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
@@ -259,11 +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--;
 	}
@@ -271,7 +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
@@ -280,109 +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;
@@ -392,9 +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;
@@ -404,7 +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;
@@ -412,41 +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;
@@ -505,9 +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)
@@ -517,7 +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;
 	}
 
@@ -525,7 +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;
 	}
 
@@ -542,17 +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);
 		}
 	}
 
@@ -568,18 +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) {
 
@@ -595,13 +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;
 	}
@@ -619,7 +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;
@@ -627,87 +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;
@@ -716,29 +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);
 
@@ -770,7 +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];
@@ -782,13 +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;
 
@@ -801,11 +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);
 	}
 }
 
@@ -819,15 +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
  *
@@ -838,29 +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;
@@ -868,87 +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;
-
-	memset(&ao_file_dirent, '\0', sizeof (struct ao_fat_dirent));
-	ao_file_offset = 0;
-	ao_file_cluster = 0;
-	ao_file_opened = 0;
+	int8_t	status;
 
-	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;
 }
 
 /*
@@ -958,17 +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
@@ -983,37 +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;
 }
 
@@ -1023,37 +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;
 }
 
@@ -1067,13 +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;
@@ -1082,11 +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;
 }
 
 /*
@@ -1099,10 +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) {
@@ -1110,66 +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 0;
-
-		if (dent[0] == AO_FAT_DENT_END) {
-			ao_fat_root_put(dent, *entry, 0);
-			return 0;
-		}
-		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 1;
-		}
-		ao_fat_root_put(dent, *entry, 0);
-		(*entry)++;
-	}
-}
-
 #if FAT_COMMANDS
 
 static const char *filesystem_errors[] = {
@@ -1188,7 +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);
@@ -1208,6 +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 {
@@ -1230,22 +1493,25 @@ 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;
 
-	while (ao_fat_readdir(&entry, &dirent)) {
+	while ((status = ao_fat_readdir(&entry, &dirent)) == AO_FAT_SUCCESS) {
 		for (i = 0; i < 8; i++)
 			putchar(dirent.name[i]);
 		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);
 	}
+	if (status != -AO_FAT_EDIREOF)
+		printf ("readdir failed: %d\n", status);
 }
 
-static uint8_t
+static void
 ao_fat_parse_name(char name[11])
 {
 	uint8_t	c;
@@ -1263,15 +1529,17 @@ ao_fat_parse_name(char name[11])
 		}
 		ao_cmd_lex();
 	}
+	while (c < 11)
+		name[c++] = ' ';
 }
 
 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') {
@@ -1279,31 +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') {
@@ -1311,9 +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();
@@ -1323,19 +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 },
 };