* file named AUTHORS, in the root directory of this distribution.
*/
/*
- * $Id: amflock.c,v 1.17.4.6.6.1 2003/10/22 17:43:33 martinea Exp $
+ * $Id: amflock.c 7161 2007-07-03 16:27:26Z dustin $
*
* file locking routines, put here to hide the system dependant stuff
* from the rest of the code
** blocking file locks as used by Amanda.
** USE_LNLOCK - Home brew exclusive, blocking file lock.
** <none> - No locking available. User beware!
-** - "configure" compiles this with -DCONFIGURE_TEST to try and determine
-** whether a particular type of locking works.
*/
+/* FIXME: This code has several limitations to be fixed:
+ * - It should be possible to select a locking mode (or detect the
+ * best mode for a particular filesystem) at runtime.
+ * - There should be a locking mode that works with NFS filesystems.
+ * - Semantics should be clear when different parts of a single
+ * process (possibly in the same/different threads) both try to lock
+ * the same file (but with different file descriptors).
+ * - It should be possible to promote a read-only lock to an
+ * exclusive lock.
+ * - Arbitrary strings should be useable as resource names. */
+
#include "amanda.h"
+/* Interface to the implementations in common-src/amflock-*.c */
-#if defined(USE_POSIX_FCNTL)
- static struct flock lock; /* zero-initialized */
+#ifdef WANT_AMFLOCK_POSIX
+extern amflock_impl_t amflock_posix_impl;
#endif
-
-#if !defined(USE_POSIX_FCNTL) && defined(USE_FLOCK)
-# ifdef HAVE_SYS_FILE_H
-# include <sys/file.h>
-# endif
-
-# if !defined(HAVE_FLOCK_DECL) && !defined(CONFIGURE_TEST)
- extern int flock P((int fd, int operation));
-# endif
+#ifdef WANT_AMFLOCK_FLOCK
+extern amflock_impl_t amflock_flock_impl;
#endif
-
-
-#if !defined(USE_POSIX_FCNTL) && !defined(USE_FLOCK) && defined(USE_LOCKF)
-
-/* XPG4-UNIX (eg, SGI IRIX, DEC DU) has F_ULOCK instead of F_UNLOCK */
-#if defined(F_ULOCK) && !defined(F_UNLOCK)
-# define F_UNLOCK F_ULOCK
+#ifdef WANT_AMFLOCK_LOCKF
+extern amflock_impl_t amflock_lockf_impl;
#endif
-
-/* Lock a file using lockf().
-** Notes:
-** - returns errors for some non-files like pipes.
-** - probably only works for files open for writing.
-*/
-int use_lockf(fd, op)
-int fd; /* fd of file to operate on */
-int op; /* true to lock; false to unlock */
-{
- off_t pos;
-
- if (op) {
- /* lock from here on */
- if (lockf(fd, F_LOCK, (off_t)0) == -1) return -1;
- }
- else {
- /* unlock from here on */
- if (lockf(fd, F_UNLOCK, (off_t)0) == -1) return -1;
-
- /* unlock from bof to here */
- pos = lseek(fd, (off_t)0, SEEK_CUR);
- if (pos == (off_t)-1) {
- if (errno == ESPIPE) pos = (off_t)0;
- else return -1;
- }
-
- if (pos > (off_t)0 &&
- lockf(fd, F_UNLOCK, -pos) == -1) return -1;
- }
-
- return 0;
-}
-
+#ifdef WANT_AMFLOCK_LNLOCK
+extern amflock_impl_t amflock_lnlock_impl;
#endif
-#if !defined(USE_POSIX_FCNTL) && !defined(USE_FLOCK) && !defined(USE_LOCKF) && defined(USE_LNLOCK)
-/* XXX - error checking in this section needs to be tightened up */
-
-/* Delete a lock file.
-*/
-int delete_lock(fn)
-char *fn;
-{
- int rc;
-
- rc = unlink(fn);
- if (rc != 0 && errno == ENOENT) rc = 0;
-
- return rc;
-}
-
-/* Create a lock file.
-*/
-int create_lock(fn, pid)
-char *fn;
-long pid;
-{
- int fd;
- FILE *f;
- int mask;
-
- (void)delete_lock(fn); /* that's MY file! */
-
- mask = umask(0027);
- fd = open(fn, O_WRONLY|O_CREAT|O_EXCL, 0640);
- umask(mask);
- if (fd == -1) return -1;
-
- if((f = fdopen(fd, "w")) == NULL) {
- aclose(fd);
- return -1;
- }
- fprintf(f, "%ld\n", pid);
- if (fclose(f) == EOF)
- return -1;
- return 0;
-}
-
-/* Read the pid out of a lock file.
-** -1=error, otherwise pid.
-*/
-long read_lock(fn)
-char *fn; /* name of lock file */
-{
- int save_errno;
- FILE *f;
- long pid;
-
- if ((f = fopen(fn, "r")) == NULL) {
- return -1;
- }
- if (fscanf(f, "%ld", &pid) != 1) {
- save_errno = errno;
- afclose(f);
- errno = save_errno;
- return -1;
- }
- if (fclose(f) != 0) {
- return -1;
- }
- return pid;
-}
-
-/* Link a lock if we can.
-** 0=done, 1=already locked, -1=error.
-*/
-int link_lock(lk, tlk)
-char *lk; /* real lock file */
-char *tlk; /* temp lock file */
-{
- int rc;
- int serrno; /* saved errno */
- struct stat lkstat, tlkstat;
-
- /* an atomic check and set operation */
- rc = link(tlk, lk);
- if (rc == 0) return 0; /* XXX do we trust it? */
-
- /* link() says it failed - don't beleive it */
- serrno = errno;
-
- if (stat(lk, &lkstat) == 0 &&
- stat(tlk, &tlkstat) == 0 &&
- lkstat.st_ino == tlkstat.st_ino)
- return 0; /* it did work! */
-
- errno = serrno;
-
- if (errno == EEXIST) rc = 1;
-
- return rc;
-}
-
-/* Steal a lock if we can.
-** 0=done; 1=still in use; -1 = error.
-*/
-int steal_lock(fn, mypid, sres)
-char *fn; /* name of lock file to steal */
-long mypid; /* my process id */
-char *sres; /* name of steal-resource to lock */
-{
- int fd;
- char buff[64];
- long pid;
- int rc;
-
- /* prevent a race with another stealer */
- rc = ln_lock(sres, 1);
- if (rc != 0) goto error;
-
- pid = read_lock(fn);
- if (pid == -1) {
- if (errno == ENOENT) goto done;
- goto error;
- }
-
- if (pid == mypid) goto steal; /* i'm the locker! */
-
- /* are they still there ? */
- rc = kill((pid_t)pid, 0);
- if (rc != 0) {
- if (errno == ESRCH) goto steal; /* locker has gone */
- goto error;
- }
-
-inuse:
- rc = ln_lock(sres, 0);
- if (rc != 0) goto error;
-
- return 1;
-
-steal:
- rc = delete_lock(fn);
- if (rc != 0) goto error;
-
-done:
- rc = ln_lock(sres, 0);
- if (rc != 0) goto error;
-
- return 0;
-
-error:
- rc = ln_lock(sres, 0);
-
- return -1;
-}
-
-/* Locking using existance of a file.
-*/
-int ln_lock(res, op)
-char *res; /* name of resource to lock */
-int op; /* true to lock; false to unlock */
-{
- long mypid;
- char *lockfile = NULL;
- char *tlockfile = NULL;
- char *mres = NULL;
- int rc;
- char pid_str[NUM_STR_SIZE];
-
- mypid = (long)getpid();
-
- lockfile = vstralloc(AMANDA_TMPDIR, "/am", res, ".lock", NULL);
-
- if (!op) {
- /* unlock the resource */
- assert(read_lock(lockfile) == mypid);
-
- (void)delete_lock(lockfile);
- amfree(lockfile);
- return 0;
- }
-
- /* lock the resource */
-
- ap_snprintf(pid_str, sizeof(pid_str), "%ld", mypid);
- tlockfile = vstralloc(AMANDA_TMPDIR, "am", res, ".", pid_str, NULL);
-
- (void)create_lock(tlockfile, mypid);
-
- mres = stralloc2(res, ".");
-
- while(1) {
- rc = link_lock(lockfile, tlockfile);
- if (rc == -1) break;
- if (rc == 0) break;
-
- rc = steal_lock(lockfile, mypid, mres);
- if (rc == -1) break;
- if (rc == 0) continue;
- sleep(1);
- }
-
- (void) delete_lock(tlockfile);
-
- amfree(mres);
- amfree(tlockfile);
- amfree(lockfile);
-
- return rc;
-}
+amflock_impl_t *amflock_impls[] = {
+#ifdef WANT_AMFLOCK_POSIX
+ &amflock_posix_impl,
#endif
-
-
-/* Get a file lock (for read-only files).
-*/
-int amroflock(fd, resource)
-int fd;
-char *resource;
-{
- int r;
-
-#ifdef USE_POSIX_FCNTL
- lock.l_type = F_RDLCK;
- lock.l_whence = SEEK_SET;
- r = fcntl(fd, F_SETLKW, &lock);
-#else
- r = amflock(fd, resource);
+#ifdef WANT_AMFLOCK_FLOCK
+ &amflock_flock_impl,
#endif
+#ifdef WANT_AMFLOCK_LOCKF
+ &amflock_lockf_impl,
+#endif
+#ifdef WANT_AMFLOCK_LNLOCK
+ &amflock_lnlock_impl,
+#endif
+ NULL
+};
- return r;
-}
-
+/* Interface functions */
+/* FIXME: for now, these just use the first non-NULL implementation
+ */
/* Get a file lock (for read/write files).
*/
-int amflock(fd, resource)
-int fd;
-char *resource;
+int
+amflock(
+ int fd,
+ char * resource)
{
- int r;
-
-#ifdef USE_POSIX_FCNTL
- lock.l_type = F_WRLCK;
- lock.l_whence = SEEK_SET;
- r = fcntl(fd, F_SETLKW, &lock);
-#else
-#ifdef USE_FLOCK
- r = flock(fd, LOCK_EX);
-#else
-#ifdef USE_LOCKF
- r = use_lockf(fd, 1);
-#else
-#ifdef USE_LNLOCK
- r = ln_lock(resource, 1);
-#else
- r = 0;
-#endif
-#endif
-#endif
-#endif
-
- return r;
+ if (!amflock_impls[0]) return 0; /* no locking */
+ return amflock_impls[0]->amflock_impl(fd, resource);
}
-
-/* Release a file lock.
-*/
-int amfunlock(fd, resource)
-int fd;
-char *resource;
+/*
+ * Get a file lock (for read-only files).
+ */
+int
+amroflock(
+ int fd,
+ char * resource)
{
- int r;
-
-#ifdef USE_POSIX_FCNTL
- lock.l_type = F_UNLCK;
- lock.l_whence = SEEK_SET;
- r = fcntl(fd, F_SETLK, &lock);
-#else
-#ifdef USE_FLOCK
- r = flock(fd, LOCK_UN);
-#else
-#ifdef USE_LOCKF
- r = use_lockf(fd, 0);
-#else
-#ifdef USE_LNLOCK
- r = ln_lock(resource, 0);
-#else
- r = 0;
-#endif
-#endif
-#endif
-#endif
-
- return r;
+ if (!amflock_impls[0]) return 0; /* no locking */
+ return amflock_impls[0]->amroflock_impl(fd, resource);
}
-
-/* Test routine for use by configure.
-** (I'm not sure why we use both return and exit!)
-** XXX the testing here should be a lot more comprehensive.
-** - lock the file and then try and lock it from another process
-** - lock the file from another process and check that process
-** termination unlocks it.
-** The hard part is to find a system independent way to not block
-** for ever.
-*/
-#ifdef CONFIGURE_TEST
-main()
+/*
+ * Release a file lock.
+ */
+int
+amfunlock(
+ int fd,
+ char * resource)
{
- int lockfd;
- char *filen = "/tmp/conftest.lock";
- char *resn = "test";
- int fd;
-
- for(fd = 3; fd < FD_SETSIZE; fd++) {
- /*
- * Make sure nobody spoofs us with a lot of extra open files
- * that would cause an open we do to get a very high file
- * descriptor, which in turn might be used as an index into
- * an array (e.g. an fd_set).
- */
- close(fd);
- }
-
- unlink(filen);
- if ((lockfd = open(filen, O_RDONLY|O_CREAT|O_EXCL, 0600)) == -1) {
- perror (filen);
- exit(10);
- }
-
- if (amroflock(lockfd, resn) != 0) {
- perror ("amroflock");
- exit(1);
- }
- if (amfunlock(lockfd, resn) != 0) {
- perror ("amfunlock/2");
- exit(2);
- }
-
- /*
- * Do not use aclose() here. During configure we do not have
- * areads_relbuf() available and it makes configure think all
- * the tests have failed.
- */
- close(lockfd);
-
- unlink(filen);
- if ((lockfd = open(filen, O_WRONLY|O_CREAT|O_EXCL, 0600)) == -1) {
- perror (filen);
- exit(20);
- }
-
- if (amflock(lockfd, resn) != 0) {
- perror ("amflock");
- exit(3);
- }
- if (amfunlock(lockfd, resn) != 0) {
- perror ("amfunlock/4");
- exit(4);
- }
-
- close(lockfd);
-
- exit(0);
+ if (!amflock_impls[0]) return 0; /* no locking */
+ return amflock_impls[0]->amfunlock_impl(fd, resource);
}
-#endif
projects / debian / amanda / blobdiff