loop: refactor: extract subfunction get_next_free_loop()

Extract subfunction get_next_free_loop() from set_loop()

Also fix miss free(try) when stat(try) and mknod fail

function                                             old     new   delta
set_loop                                             807     790     -17

Fixes: 3448914e8cc5 ("mount,losetup: use /dev/loop-control is it exists")
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 26 insertions, 30 deletions

diff --git a/libbb/loop.c b/libbb/loop.c
index 750642ade..8e5c915fc 100644
--- a/libbb/loop.c
+++ b/libbb/loop.c
@@ -96,6 +96,20 @@ int FAST_FUNC get_free_loop(void)
         return loopdevno; /* can be -1 if error */
 }
 
+static int get_next_free_loop(char *dev, int id)
+{
+        int loopdevno;
+
+        loopdevno = get_free_loop();
+        if (loopdevno != -1) {
+                /* loopdevno is -2 (use id) or >= 0 (use id = loopdevno): */
+                if (loopdevno >= 0)
+                        id = loopdevno;
+                sprintf(dev, LOOP_FORMAT, id);
+        }
+        return loopdevno;
+}
+
 /* 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.
@@ -123,30 +137,27 @@ 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 == -1) {
-                        close(ffd);
-                        return -1; /* no free loop devices */
-                }
-                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;
         }
 
         /* 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 (!*device) {
+                        rc = get_next_free_loop(dev, i);
+                        if (rc == -1)
+                                break; /* no free loop devices (or other error in LOOP_CTL_GET_FREE) */
+                        if (rc >= 0)
+                                /* /dev/loop-control gave us the next free /dev/loopN */
+                                goto open_lfd;
+                        /* else: sequential /dev/loopN, needs to be tested/maybe_created */
+                }
 
                 IF_FEATURE_MOUNT_LOOP_CREATE(errno = 0;)
                 if (stat(try, &statbuf) != 0 || !S_ISBLK(statbuf.st_mode)) {
                         if (ENABLE_FEATURE_MOUNT_LOOP_CREATE
                          && errno == ENOENT
-                         && try == dev
+                         && (!*device)
                         ) {
                                 /* Node doesn't exist, try to create it */
                                 if (mknod(dev, S_IFBLK|0644, makedev(7, i)) == 0)
@@ -179,13 +190,10 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
                         /* 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);
+                                if (!*device) {
                                         close(lfd);
 //TODO: add "if (--failcount != 0) ..."?
-                                        goto get_free_loopN;
+                                        continue;
                                 }
                                 goto close_and_try_next_loopN;
                         }
@@ -209,8 +217,6 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
                         }
                         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 */
@@ -218,16 +224,6 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
                         }
                         /* failure, undo LOOP_SET_FD */
                         ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
-                } else {
-                        /* device is not free (rc == 0), or error other than ENXIO */
-                        if (rc == 0     /* device is not free? */
-                         && !*device    /* racing with other mount? */
-                         && try != dev  /* tried a _kernel-offered_ loopN? */
-                        ) {
-                                free(try);
-                                close(lfd);
-                                goto get_free_loopN;
-                        }
                 }
  close_and_try_next_loopN:
                 close(lfd);