On 06/10/2015 11:11 AM, Stanislav Kholmanskikh wrote:
On systems employing the "lazy loop device removal",
kernel commit commit a1ecac3b0656a68259927c234e505804d33a7b83
("loop: Make explicit loop device destruction lazy"),
ioctl(LOOP_CLR_FD) may return 0 when the loop device is in use,
for example by udev.
Therefore, there is a chance that a quick attach/detach may not
give udev enough time to complete, like this:
open("file.img", O_RDWR) = 4
ioctl(3, LOOP_SET_FD, 0x4) = 0
close(3) = 0
close(4) = 0
open("/dev/loop0", O_RDONLY) = 3
ioctl(3, LOOP_CLR_FD, 0) = 0
close(3) = 0
open("/dev/loop0", O_RDWR) = 3
open("file.img", O_RDWR) = 4
ioctl(3, LOOP_SET_FD, 0x4) = -1 EBUSY (Device or resource busy)
So let's wait until the kernel frees the loop device, i.e.
when ioctl(LOOP_CLR_FD) starts failing with ENXIO.
Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmansk...@oracle.com>
I tested it the attached test case (plus you need to remove 'static'
next to attach_device and detach_device).
Without the patch it fails with:
[root@kholmanskikh test]# ./loop_test
loop_test 1 TBROK : tst_device.c:144: ioctl(/dev/loop0,
LOOP_SET_FD, file.img) failed: EBUSY
loop_test 2 TBROK : tst_device.c:144: Remaining cases broken
#include "test.h"
#include "safe_macros.h"
char *TCID = "loop_test";
int TST_TOTAL = 1;
void attach_device(void (*cleanup_fn)(void),
const char *dev, const char *file);
void detach_device(void (*cleanup_fn)(void), const char *dev);
int main(void)
{
int i, fd;
tst_tmpdir();
fd = SAFE_OPEN(NULL, "file.img", O_RDWR | O_CREAT, 0644);
SAFE_FTRUNCATE(NULL, fd, 1024 * 1024UL);
SAFE_CLOSE(NULL, fd);
for (i = 0; i < 1000; i++) {
attach_device(NULL, "/dev/loop0", "file.img");
detach_device(NULL, "/dev/loop0");
}
tst_rmdir();
tst_resm(TPASS, "Finished");
tst_exit();
}
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