14.12.2021 15:03, Karel Zak wrote:
Hi Vladimir,
On Thu, Dec 09, 2021 at 03:12:33PM +0100, Vladimir Sementsov-Ogievskiy wrote:
Note, that this commit is done as a "minimal change", i.e. I only try to
rollback O_NONBLOCK for floppy. The other way is to detect CDROM
instead, and reopen with original flags for everything except CDROM.
I also tried fcntl instead of close/open, and that didn't help.
What does it mean didn't help?
I tried it, but the bug remains as it was.. As I understand, dropping O_NONBLOCK by fcntl just removes this flag, to change further behavior of device to non-blocking. But it doesn't do any additional actions in driver.
In floppy.c the only place where FMODE_NDELAY take place is floppy_open(). So, we want to change the behavior exactly of thet open() call. As I understand fcntl() doesn't trigger floppy_open() call, that's why it can't help.
I guess that drop O_NONBLOCk in blkid_probe_set_device() for floppies
would be enough, something like:
int blkid_probe_set_device(blkid_probe pr, int fd,
blkid_loff_t off, blkid_loff_t size)
{
...
if (ioctl(fd, FDGETDRVTYP, &name) >= 0) {
int flags;
if ((flags = fcntl(fd, F_GETFL, 0)) != -1)
fcntl(fd, F_SETFL, flags & ~O_NONBLOCK);
}
...
}
Yes, it's a little bit dirty to modify FD in the library (if the FD is
provided by the application), but if O_NONBLOCK is wrong in all cases for
floppies, then it seems like a good thing.
This solution will fix the problem without libblkid API change, and it
will fix it in all current applications.
The solution based on blkid_safe_open() means that we have to modify
many applications. For example, systemd/udevd uses
fd = open(devnode, O_RDONLY|O_CLOEXEC|O_NONBLOCK);
r = blkid_probe_set_device(pr, fd, offset, 0);
Hmm, yes, that's not very good :(
The same is probably in many other places (mkfs-like programs, etc.).
What do you think?
Maybe be we can get filename from fd reading it from /proc, then do open() and than dup() to old fd.. But that's even more dirty to do in a library call.
--
Best regards,
Vladimir
