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losetup: use loop-control to explicitly ask for device 

Now we use LOOP_CTL_GET_FREE ioctl to ask for free device, for example

  losetup -f foo.img

Unfortunately, losetup(8) allows to ask for specified device

  losetup /dev/loop100 foo.img

and in this case we assume that the device already exists in the
system. This is incorrect, we should be able to use loop-control
LOOP_CTL_ADD ioctl to ask for the specified device.

Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2013-08-06 11:04:35 +02:00
parent 777519226d
commit 3cb2413b02
3 changed files with 33 additions and 0 deletions
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1
include/loopdev.h
View File

@ -149,6 +149,7 @@ extern void loopcxt_enable_debug(struct loopdev_cxt *lc, int enable);
extern int loopcxt_set_device(struct loopdev_cxt *lc, const char *device)
__attribute__ ((warn_unused_result));
extern int loopcxt_has_device(struct loopdev_cxt *lc);
extern int loopcxt_add_device(struct loopdev_cxt *lc);
extern char *loopcxt_strdup_device(struct loopdev_cxt *lc);
extern const char *loopcxt_get_device(struct loopdev_cxt *lc);
extern struct sysfs_cxt *loopcxt_get_sysfs(struct loopdev_cxt *lc);

30
lib/loopdev.c
View File

@ -1297,6 +1297,36 @@ int loopcxt_delete_device(struct loopdev_cxt *lc)
return 0;
}
int loopcxt_add_device(struct loopdev_cxt *lc)
{
int rc = -EINVAL;
int ctl, nr = -1;
const char *p, *dev = loopcxt_get_device(lc);
if (!dev)
goto done;
if (!(lc->flags & LOOPDEV_FL_CONTROL)) {
rc = -ENOSYS;
goto done;
}
p = strrchr(dev, '/');
if (!p || (sscanf(p, "/loop%d", &nr) != 1 && sscanf(p, "/%d", &nr) != 1)
|| nr < 0)
goto done;
ctl = open(_PATH_DEV_LOOPCTL, O_RDWR|O_CLOEXEC);
if (ctl >= 0) {
DBG(lc, loopdev_debug("add_device %d", nr));
rc = ioctl(ctl, LOOP_CTL_ADD, nr);
close(ctl);
}
done:
DBG(lc, loopdev_debug("add_device done [rc=%d]", rc));
return rc;
}
/*
* Note that LOOP_CTL_GET_FREE ioctl is supported since kernel 3.1. In older
* kernels we have to check all loop devices to found unused one.

2
sys-utils/losetup.c
View File

@ -641,6 +641,8 @@ int main(int argc, char **argv)
{
int hasdev = loopcxt_has_device(&lc);
if (hasdev && !is_loopdev(loopcxt_get_device(&lc)))
loopcxt_add_device(&lc);
do {
const char *errpre;