[Qemu-block] [PATCH for-2.10? v3 0/2] block: Do OFD lock check at runtime

[Fam Zheng]

v3: Fix mingw build. [patchew]

v2: Probe /dev/null to save LOC. [Eric]
    Mention "new glibc + old kernel" in commit message. [Kevin, Daniel, Eric,
    Christian]

This fixes the image opening failure reported by Andrew Baumann:

> I'm running a recent Linux build of qemu on Windows Subsystem for Linux (WSL)
> which doesn't appear to implement file locking:
>
> $ 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

It appears to be that the binary is built for Linux targets, but the WSL
runtime doesn't recognize the ops (-EINVAL).

This is also a practical problem for Linux considering it's possible to run
QEMU which is built against a new glibc on an old kernel that doesn't have OFD
API.

Convert to runtime check to cope with that.

Fam Zheng (2):
  osdep: Add runtime OFD lock detection
  file-posix: Do runtime check for ofd lock API

 block/file-posix.c   | 19 +++++++--------
 include/qemu/osdep.h |  1 +
 util/osdep.c         | 66 ++++++++++++++++++++++++++++++++++++++++++++--------
 3 files changed, 65 insertions(+), 21 deletions(-)

-- 
2.13.4