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block: Separate blk_is_writable() and blk_supports_write_perm()

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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>
Message-Id: <20210118123448.307825-2-kwolf@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2021-01-18 13:34:47 +01:00
parent bf159f0bdc
commit 86b1cf3227
20 changed files with 57 additions and 41 deletions
Download patch file Download diff file Expand all files Collapse all files

6
hw/block/virtio-blk.c
View file

@ -1021,7 +1021,7 @@ static uint64_t virtio_blk_get_features(VirtIODevice *vdev, uint64_t features,
virtio_has_feature(features, VIRTIO_BLK_F_CONFIG_WCE))) {
virtio_add_feature(&features, VIRTIO_BLK_F_WCE);
}
if (blk_is_read_only(s->blk)) {
if (!blk_is_writable(s->blk)) {
virtio_add_feature(&features, VIRTIO_BLK_F_RO);
}
if (s->conf.num_queues > 1) {
@ -1175,8 +1175,8 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
}
if (!blkconf_apply_backend_options(&conf->conf,
blk_is_read_only(conf->conf.blk), true,
errp)) {
!blk_supports_write_perm(conf->conf.blk),
true, errp)) {
return;
}
s->original_wce = blk_enable_write_cache(conf->conf.blk);