diff options
| -rw-r--r-- | libbb/loop.c | 138 |
1 files changed, 73 insertions, 65 deletions
diff --git a/libbb/loop.c b/libbb/loop.c index 85b2724..1539909 100644 --- a/libbb/loop.c +++ b/libbb/loop.c @@ -98,9 +98,7 @@ int FAST_FUNC get_free_loop(void) /* Returns opened fd to the loop device, <0 on error. * *device is loop device to use, or if *device==NULL finds a loop device to - * mount it on and sets *device to a strdup of that loop device name. This - * search will re-use an existing loop device already bound to that - * file/offset if it finds one. + * mount it on and sets *device to a strdup of that loop device name. */ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset, unsigned long long sizelimit, unsigned flags) @@ -109,9 +107,7 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse char *try; bb_loop_info loopinfo; struct stat statbuf; - int i, dfd, ffd, mode, rc; - - rc = dfd = -1; + int i, lfd, ffd, mode, rc; /* Open the file. Barf if this doesn't work. */ mode = (flags & BB_LO_FLAGS_READ_ONLY) ? O_RDONLY : O_RDWR; @@ -127,24 +123,23 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse try = *device; if (!try) { + get_free_loopN: i = get_free_loop(); - if (i == -2) { /* no /dev/loop-control */ - i = 0; - try = dev; - goto old_style; - } if (i == -1) { close(ffd); return -1; /* no free loop devices */ } - try = *device = xasprintf(LOOP_FORMAT, i); - goto try_to_open; + if (i >= 0) { + try = xasprintf(LOOP_FORMAT, i); + goto open_lfd; + } + /* i == -2: no /dev/loop-control. Do an old-style search for a free device */ + try = dev; } - old_style: - /* Find a loop device. */ - /* 1048575 (0xfffff) is a max possible minor number in Linux circa 2010 */ - for (i = 0; rc && i < 1048576; i++) { + /* Find a loop device */ + /* 0xfffff is a max possible minor number in Linux circa 2010 */ + for (i = 0; i <= 0xfffff; i++) { sprintf(dev, LOOP_FORMAT, i); IF_FEATURE_MOUNT_LOOP_CREATE(errno = 0;) @@ -153,72 +148,85 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse && errno == ENOENT && try == dev ) { - /* Node doesn't exist, try to create it. */ + /* Node doesn't exist, try to create it */ if (mknod(dev, S_IFBLK|0644, makedev(7, i)) == 0) - goto try_to_open; + goto open_lfd; } - /* Ran out of block devices, return failure. */ + /* Ran out of block devices, return failure */ rc = -1; break; } - try_to_open: - /* Open the sucker and check its loopiness. */ - dfd = open(try, mode); - if (dfd < 0 && errno == EROFS) { + open_lfd: + /* Open the sucker and check its loopiness */ + lfd = rc = open(try, mode); + if (lfd < 0 && errno == EROFS) { mode = O_RDONLY; - dfd = open(try, mode); + lfd = rc = open(try, mode); } - if (dfd < 0) { + if (lfd < 0) { if (errno == ENXIO) { /* Happens if loop module is not loaded */ - rc = -1; + /* rc is -1; */ break; } - goto try_again; + goto try_next_loopN; } - rc = ioctl(dfd, BB_LOOP_GET_STATUS, &loopinfo); + rc = ioctl(lfd, BB_LOOP_GET_STATUS, &loopinfo); - /* If device is free, claim it. */ + /* If device is free, try to claim it */ if (rc && errno == ENXIO) { - /* Associate free loop device with file. */ - if (ioctl(dfd, LOOP_SET_FD, ffd) == 0) { - memset(&loopinfo, 0, sizeof(loopinfo)); - safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE); - loopinfo.lo_offset = offset; - loopinfo.lo_sizelimit = sizelimit; - /* - * Used by mount to set LO_FLAGS_AUTOCLEAR. - * LO_FLAGS_READ_ONLY is not set because RO is controlled by open type of the file. - * Note that closing LO_FLAGS_AUTOCLEARed dfd before mount - * is wrong (would free the loop device!) - */ - loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY); - rc = ioctl(dfd, BB_LOOP_SET_STATUS, &loopinfo); - if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) { - /* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */ - /* (this code path is not tested) */ - loopinfo.lo_flags -= BB_LO_FLAGS_AUTOCLEAR; - rc = ioctl(dfd, BB_LOOP_SET_STATUS, &loopinfo); - } - if (rc != 0) { - ioctl(dfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary + /* Associate free loop device with file */ + if (ioctl(lfd, LOOP_SET_FD, ffd)) { + /* Ouch. Are we racing with other mount? */ + if (!*device /* yes */ + && try != dev /* tried a _kernel-offered_ loopN? */ + ) { + free(try); + close(lfd); +//TODO: add "if (--failcount != 0) ..."? + goto get_free_loopN; } + goto try_next_loopN; } - } else { - rc = -1; - } - if (rc != 0) { - close(dfd); + memset(&loopinfo, 0, sizeof(loopinfo)); + safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE); + loopinfo.lo_offset = offset; + loopinfo.lo_sizelimit = sizelimit; + /* + * Used by mount to set LO_FLAGS_AUTOCLEAR. + * LO_FLAGS_READ_ONLY is not set because RO is controlled by open type of the file. + * Note that closing LO_FLAGS_AUTOCLEARed lfd before mount + * is wrong (would free the loop device!) + */ + loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY); + rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo); + if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) { + /* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */ + /* (this code path is not tested) */ + loopinfo.lo_flags -= BB_LO_FLAGS_AUTOCLEAR; + rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo); + } + if (rc == 0) { + /* SUCCESS! */ + if (try != dev) /* tried a kernel-offered free loopN? */ + *device = try; /* malloced */ + if (!*device) /* was looping in search of free "/dev/loopN"? */ + *device = xstrdup(dev); + rc = lfd; /* return this */ + break; + } + /* failure, undo LOOP_SET_FD */ + ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary } - try_again: - if (*device) break; - } + /* else: device is not free (rc == 0) or error other than ENXIO */ + close(lfd); + try_next_loopN: + rc = -1; + if (*device) /* was looking for a particular "/dev/loopN"? */ + break; /* yes, do not try other names */ + } /* for() */ + close(ffd); - if (rc == 0) { - if (!*device) - *device = xstrdup(dev); - return dfd; - } return rc; } |