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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

9
hw/block/fdc.c
View file

@ -444,7 +444,7 @@ static void fd_revalidate(FDrive *drv)
FLOPPY_DPRINTF("revalidate\n");
if (drv->blk != NULL) {
drv->ro = blk_is_read_only(drv->blk);
drv->ro = !blk_is_writable(drv->blk);
if (!blk_is_inserted(drv->blk)) {
FLOPPY_DPRINTF("No disk in drive\n");
drv->disk = FLOPPY_DRIVE_TYPE_NONE;
@ -479,8 +479,8 @@ static void fd_change_cb(void *opaque, bool load, Error **errp)
blk_set_perm(drive->blk, 0, BLK_PERM_ALL, &error_abort);
} else {
if (!blkconf_apply_backend_options(drive->conf,
blk_is_read_only(drive->blk), false,
errp)) {
!blk_supports_write_perm(drive->blk),
false, errp)) {
return;
}
}
@ -553,7 +553,8 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp)
* read-only node later */
read_only = true;
} else {
read_only = !blk_bs(dev->conf.blk) || blk_is_read_only(dev->conf.blk);
read_only = !blk_bs(dev->conf.blk) ||
!blk_supports_write_perm(dev->conf.blk);
}
if (!blkconf_blocksizes(&dev->conf, errp)) {