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

[Olaf Seibert]

Public bug reported:

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.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1865048

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

Status in QEMU:
  New

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.

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