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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
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3
include/sysemu/block-backend.h
View file

@ -191,7 +191,8 @@ BlockErrorAction blk_get_error_action(BlockBackend *blk, bool is_read,
int error);
void blk_error_action(BlockBackend *blk, BlockErrorAction action,
bool is_read, int error);
bool blk_is_read_only(BlockBackend *blk);
bool blk_supports_write_perm(BlockBackend *blk);
bool blk_is_writable(BlockBackend *blk);
bool blk_is_sg(BlockBackend *blk);
bool blk_enable_write_cache(BlockBackend *blk);
void blk_set_enable_write_cache(BlockBackend *blk, bool wce);