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loop-util: invoke LOOP_CTL_GET_FREE in a loop

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if we don't call it in a loop the device it tells us to open might
already be gone, taken by somebody else racing against us. Hence try a
few times.
This commit is contained in:
Lennart Poettering 2019-05-21 18:13:55 +02:00 committed by Zbigniew Jędrzejewski-Szmek
parent 0307afc681
commit 0f6519d43c
1 changed files with 23 additions and 10 deletions
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33
src/shared/loop-util.c
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@ -18,6 +18,7 @@ int loop_device_make(int fd, int open_flags, LoopDevice **ret) {
_cleanup_close_ int control = -1, loop = -1;
_cleanup_free_ char *loopdev = NULL;
unsigned n_attempts = 0;
struct stat st;
LoopDevice *d;
int nr, r;
@ -60,19 +61,31 @@ int loop_device_make(int fd, int open_flags, LoopDevice **ret) {
if (control < 0)
return -errno;
nr = ioctl(control, LOOP_CTL_GET_FREE);
if (nr < 0)
return -errno;
/* Loop around LOOP_CTL_GET_FREE, since at the moment we attempt to open the returned device it might
* be gone already, taken by somebody else racing against us. */
for (;;) {
nr = ioctl(control, LOOP_CTL_GET_FREE);
if (nr < 0)
return -errno;
if (asprintf(&loopdev, "/dev/loop%i", nr) < 0)
return -ENOMEM;
if (asprintf(&loopdev, "/dev/loop%i", nr) < 0)
return -ENOMEM;
loop = open(loopdev, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
if (loop < 0)
return -errno;
loop = open(loopdev, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
if (loop < 0)
return -errno;
if (ioctl(loop, LOOP_SET_FD, fd) < 0) {
if (errno != EBUSY)
return -errno;
if (ioctl(loop, LOOP_SET_FD, fd) < 0)
return -errno;
if (++n_attempts >= 64) /* Give up eventually */
return -EBUSY;
} else
break;
loopdev = mfree(loopdev);
loop = safe_close(loop);
}
if (ioctl(loop, LOOP_SET_STATUS64, &info) < 0)
return -errno;