Commit 2b218f5d authored by Fam Zheng's avatar Fam Zheng Committed by Kevin Wolf
Browse files

file-posix: Do runtime check for ofd lock API 



It is reported that on Windows Subsystem for Linux, ofd operations fail
with -EINVAL. In other words, QEMU binary built with system headers that
exports F_OFD_SETLK doesn't necessarily run in an environment that
actually supports it:

$ qemu-system-aarch64 ... -drive file=test.vhdx,if=none,id=hd0 \
    -device virtio-blk-pci,drive=hd0
qemu-system-aarch64: -drive file=test.vhdx,if=none,id=hd0: Failed to unlock byte 100
qemu-system-aarch64: -drive file=test.vhdx,if=none,id=hd0: Failed to unlock byte 100
qemu-system-aarch64: -drive file=test.vhdx,if=none,id=hd0: Failed to lock byte 100

As a matter of fact this is not WSL specific. It can happen when running
a QEMU compiled against a newer glibc on an older kernel, such as in
a containerized environment.

Let's do a runtime check to cope with that.

Reported-by: default avatarAndrew Baumann <Andrew.Baumann@microsoft.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Signed-off-by: default avatarFam Zheng <famz@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent ca749954

block/file-posix.c

+8 −11
Original line number Diff line number Diff line
@@ -457,22 +457,19 @@ static int raw_open_common(BlockDriverState *bs, QDict *options, 
    switch (locking) {

    case ON_OFF_AUTO_ON:

        s->use_lock = true;

#ifndef F_OFD_SETLK

        if (!qemu_has_ofd_lock()) {

            fprintf(stderr,

                "File lock requested but OFD locking syscall is unavailable, "

                "falling back to POSIX file locks.\n"

                "Due to the implementation, locks can be lost unexpectedly.\n");

#endif

                    "File lock requested but OFD locking syscall is "

                    "unavailable, falling back to POSIX file locks.\n"

                    "Due to the implementation, locks can be lost "

                    "unexpectedly.\n");

        }

        break;

    case ON_OFF_AUTO_OFF:

        s->use_lock = false;

        break;

    case ON_OFF_AUTO_AUTO:

#ifdef F_OFD_SETLK

        s->use_lock = true;

#else

        s->use_lock = false;

#endif

        s->use_lock = qemu_has_ofd_lock();

        break;

    default:

        abort();