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Diffstat (limited to 'libbb/loop.c')
-rw-r--r--libbb/loop.c42
1 files changed, 36 insertions, 6 deletions
diff --git a/libbb/loop.c b/libbb/loop.c
index c78535a..ada0c76 100644
--- a/libbb/loop.c
+++ b/libbb/loop.c
@@ -78,6 +78,24 @@ int FAST_FUNC del_loop(const char *device)
return rc;
}
+/* Obtain an unused loop device number */
+int FAST_FUNC get_free_loop(void)
+{
+ int fd;
+ int loopdevno;
+
+ fd = open("/dev/loop-control", O_RDWR | O_CLOEXEC);
+ if (fd == -1)
+ return fd - 1; /* -2: "no /dev/loop-control" */
+
+#ifndef LOOP_CTL_GET_FREE
+# define LOOP_CTL_GET_FREE 0x4C82
+#endif
+ loopdevno = ioctl(fd, LOOP_CTL_GET_FREE);
+ close(fd);
+ return loopdevno; /* can be -1 if error */
+}
+
/* 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
@@ -106,12 +124,24 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
return -errno;
}
-//TODO: use LOOP_CTL_GET_FREE instead of trying every loopN in sequence? a-la:
-// fd = open("/dev/loop-control", O_RDWR);
-// loopN = ioctl(fd, LOOP_CTL_GET_FREE);
-//
+ try = *device;
+ if (!try) {
+ 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;
+ }
+
+ old_style:
/* Find a loop device. */
- try = *device ? *device : dev;
/* 1048575 (0xfffff) is a max possible minor number in Linux circa 2010 */
for (i = 0; rc && i < 1048576; i++) {
sprintf(dev, LOOP_FORMAT, i);
@@ -170,7 +200,7 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
rc = ioctl(dfd, BB_LOOP_SET_STATUS, &loopinfo);
}
if (rc != 0) {
- ioctl(dfd, LOOP_CLR_FD, 0);
+ ioctl(dfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
}
}
} else {