Re: [PATCH 1/2] block: Separate blk_is_writable() and blk_supports_write_perm()

[Philippe Mathieu-Daudé]

On 1/18/21 1:34 PM, Kevin Wolf wrote:
> Currently, blk_is_read_only() tells whether a given BlockBackend can
> only be used in read-only mode because its root node is read-only. Some
> callers actually try to answer a slightly different question: Is the
> BlockBackend configured to be writable, by taking write permissions on
> the root node?
> 
> This can differ, for example, for CD-ROM devices which don't take write
> permissions, but may be backed by a writable image file. scsi-cd allows
> write requests to the drive if blk_is_read_only() returns false.
> However, the write request will immediately run into an assertion
> failure because the write permission is missing.
> 
> This patch introduces separate functions for both questions.
> blk_supports_write_perm() answers the question whether the block
> node/image file can support writable devices, whereas blk_is_writable()
> tells whether the BlockBackend is currently configured to be writable.
> 
> All calls of blk_is_read_only() are converted to one of the two new
> functions.
> 
> Fixes: https://bugs.launchpad.net/bugs/1906693
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/sysemu/block-backend.h |  3 ++-
>  block/block-backend.c          | 19 ++++++++++++++++---
>  hw/block/dataplane/xen-block.c |  2 +-
>  hw/block/fdc.c                 |  9 +++++----
>  hw/block/m25p80.c              |  6 +++---
>  hw/block/nand.c                |  2 +-
>  hw/block/nvme-ns.c             |  7 ++++---
>  hw/block/onenand.c             |  2 +-
>  hw/block/pflash_cfi01.c        |  2 +-
>  hw/block/pflash_cfi02.c        |  2 +-
>  hw/block/swim.c                |  6 +++---
>  hw/block/virtio-blk.c          |  6 +++---
>  hw/block/xen-block.c           |  2 +-
>  hw/ide/core.c                  |  2 +-
>  hw/misc/sifive_u_otp.c         |  2 +-
>  hw/ppc/pnv_pnor.c              |  2 +-
>  hw/scsi/scsi-disk.c            | 10 +++++-----
>  hw/scsi/scsi-generic.c         |  4 ++--
>  hw/sd/sd.c                     |  6 +++---
>  hw/usb/dev-storage.c           |  4 ++--
>  20 files changed, 57 insertions(+), 41 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>