block: Separate blk_is_writable() and blk_supports_write_perm()

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>

2 files changed, 7 insertions, 7 deletions

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 29504ea081..ed52fcd49f 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -1270,7 +1270,7 @@ static int scsi_disk_emulate_mode_sense(SCSIDiskReq *r, uint8_t *outbuf)
 
     if (s->qdev.type == TYPE_DISK) {
         dev_specific_param = s->features & (1 << SCSI_DISK_F_DPOFUA) ? 0x10 : 0;
-        if (blk_is_read_only(s->qdev.conf.blk)) {
+        if (!blk_is_writable(s->qdev.conf.blk)) {
             dev_specific_param |= 0x80; /* Readonly.  */
         }
     } else {
@@ -1704,7 +1704,7 @@ static void scsi_disk_emulate_unmap(SCSIDiskReq *r, uint8_t *inbuf)
         goto invalid_param_len;
     }
 
-    if (blk_is_read_only(s->qdev.conf.blk)) {
+    if (!blk_is_writable(s->qdev.conf.blk)) {
         block_acct_invalid(blk_get_stats(s->qdev.conf.blk), BLOCK_ACCT_UNMAP);
         scsi_check_condition(r, SENSE_CODE(WRITE_PROTECTED));
         return;
@@ -1795,7 +1795,7 @@ static void scsi_disk_emulate_write_same(SCSIDiskReq *r, uint8_t *inbuf)
         return;
     }
 
-    if (blk_is_read_only(s->qdev.conf.blk)) {
+    if (!blk_is_writable(s->qdev.conf.blk)) {
         scsi_check_condition(r, SENSE_CODE(WRITE_PROTECTED));
         return;
     }
@@ -2207,7 +2207,7 @@ static int32_t scsi_disk_dma_command(SCSIRequest *req, uint8_t *buf)
     case WRITE_VERIFY_10:
     case WRITE_VERIFY_12:
     case WRITE_VERIFY_16:
-        if (blk_is_read_only(s->qdev.conf.blk)) {
+        if (!blk_is_writable(s->qdev.conf.blk)) {
             scsi_check_condition(r, SENSE_CODE(WRITE_PROTECTED));
             return 0;
         }
@@ -2380,7 +2380,7 @@ static void scsi_realize(SCSIDevice *dev, Error **errp)
         }
     }
 
-    read_only = blk_is_read_only(s->qdev.conf.blk);
+    read_only = !blk_supports_write_perm(s->qdev.conf.blk);
     if (dev->type == TYPE_ROM) {
         read_only = true;
     }
diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index 9740f7e36a..ab220141f5 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -306,7 +306,7 @@ static void scsi_read_complete(void * opaque, int ret)
      * readonly.
      */
     if ((s->type == TYPE_DISK || s->type == TYPE_TAPE || s->type == TYPE_ZBC) &&
-        blk_is_read_only(s->conf.blk) &&
+        !blk_is_writable(s->conf.blk) &&
         (r->req.cmd.buf[0] == MODE_SENSE ||
          r->req.cmd.buf[0] == MODE_SENSE_10) &&
         (r->req.cmd.buf[1] & 0x8) == 0) {
@@ -694,7 +694,7 @@ static void scsi_generic_realize(SCSIDevice *s, Error **errp)
         return;
     }
     if (!blkconf_apply_backend_options(&s->conf,
-                                       blk_is_read_only(s->conf.blk),
+                                       !blk_supports_write_perm(s->conf.blk),
                                        true, errp)) {
         return;
     }