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udev/cdrom_id: Do not open CD-rom in exclusive mode.

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When you have a CD automunt solution that talks directly to the kernel
independently of udev it races with cdrom_id for exclusive access to the
device failing unpredictably.

The whole is_mounted function in cdrom_id is broken: there is no saying
what happens between calling is_mounted and opening the device.

Hence assume that the device can be mounted asynchronously at any time,
do not use exclusive access, and do away with is_mouted.

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
This commit is contained in:
Michal Suchanek 2019-10-20 12:12:20 +02:00 committed by Zbigniew Jędrzejewski-Szmek
parent 69ec2fdd9c
commit 14cd12b3d5
1 changed files with 1 additions and 23 deletions
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24
src/udev/cdrom_id/cdrom_id.c
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@ -85,28 +85,6 @@ static unsigned long long int cd_media_session_last_offset;
#define ASC(errcode) (((errcode) >> 8) & 0xFF)
#define ASCQ(errcode) ((errcode) & 0xFF)
static bool is_mounted(const char *device) {
struct stat statbuf;
FILE *fp;
int maj, min;
bool mounted = false;
if (stat(device, &statbuf) < 0)
return false;
fp = fopen("/proc/self/mountinfo", "re");
if (!fp)
return false;
while (fscanf(fp, "%*s %*s %i:%i %*[^\n]", &maj, &min) == 2) {
if (makedev(maj, min) == statbuf.st_rdev) {
mounted = true;
break;
}
}
fclose(fp);
return mounted;
}
static void info_scsi_cmd_err(const char *cmd, int err) {
if (err == -1)
log_debug("%s failed", cmd);
@ -874,7 +852,7 @@ int main(int argc, char *argv[]) {
for (cnt = 20; cnt > 0; cnt--) {
struct timespec duration;
fd = open(node, O_RDONLY|O_NONBLOCK|O_CLOEXEC|(is_mounted(node) ? 0 : O_EXCL));
fd = open(node, O_RDONLY|O_NONBLOCK|O_CLOEXEC);
if (fd >= 0 || errno != EBUSY)
break;
duration.tv_sec = 0;