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file-posix: Do runtime check for ofd lock API

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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: Andrew Baumann <Andrew.Baumann@microsoft.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fam Zheng 2017-08-11 19:44:47 +08:00 committed by Kevin Wolf
parent ca749954b0
commit 2b218f5dbc
1 changed files with 8 additions and 11 deletions
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19
block/file-posix.c
View file

@ -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
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
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");
}
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();