[Bug 1865048] Re: qemu-img --force-share does not disable file locking

[Olaf Seibert]

Hi Maz,

thanks for the information!

The situation we're in is where we are suspecting the file locking on a
shared network file system to be broken, so we were looking for ways to
avoid any locking. I had tried some variations on your image-opts style
invocation, but did not find any variant where the automatic file format
detection would be preserved. For instance, with --image-opts
driver=file,filename=foo.qcow2,locking=off it would think the file is
raw. But the one you give seems to do what I want to experiment with, so
thanks again!

-Olaf.

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1865048

Title:
  qemu-img --force-share does not disable file locking

Status in QEMU:
  Invalid

Bug description:
  The new option "--force-share" for qemu-img does not disable file
  locking.

  I tried it with version qemu-img version 2.11.1(Debian 1:2.11+dfsg-
  1ubuntu7.21~cloud0) and I traced the source code of the current git
  trunk.

  Sample to demonstrate:

  # strace qemu-img info --force-share testfile.qcow2   2>&1 | grep F_RDLCK
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0
  fcntl(11, F_OFD_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=100, 
l_len=1}) = 0

  I traced the passing of the --force-share option through the source
  code (I used commit 6c599282f8 as of Mon Feb 17 13:32:25 2020 +0000)

  qemu-img.c:img_info()
          force_share = true;
  qemu-img.c:collect_image_info_list(force_share)
  qemu-img.c:img_open(force_share)
  qemu-img.c:img_open_file(force_share)
          qdict_put_bool(options, BDRV_OPT_FORCE_SHARE, true);
  block/block-backend.c:blk_new_open(options)
  block.c:bdrv_open(options)
  block.c:bdrv_open_inheritoptions()
  block.c:bdrv_open_common(options)
          bs->force_share = qemu_opt_get_bool(opts, BDRV_OPT_FORCE_SHARE, 
false);
  block.c:bdrv_open_driver(bs)
  include/block/block_int.h:int (*bdrv_file_open)(BlockDriverState *bs, QDict 
*options, int flags,
  block/file-posix.c:.bdrv_file_open = raw_open,
  block/file-posix.c:raw_open_common(bs)
          locking = qapi_enum_parse(&OnOffAuto_lookup,
                                qemu_opt_get(opts, "locking"),
                                ON_OFF_AUTO_AUTO, &local_err);
          ignoring bs->force_share

  At the end, bs->force_share is ignored in determining the locking
  value.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1865048/+subscriptions