file-posix: Fix bdrv_open_flags() for snapshot=on

Using a different read-only setting for bs->open_flags than for the
flags to the driver's open function is just inconsistent and a bad idea.
After this patch, the temporary snapshot keeps being opened read-only if
read-only=on,snapshot=on is passed.

If we wanted to change this behaviour to make only the orginal image
file read-only, but the temporary overlay read-write (as the comment in
the removed code suggests), that change would have to be made in
bdrv_temp_snapshot_options() (where the comment suggests otherwise).

Addressing this inconsistency before introducing dynamic auto-read-only
is important because otherwise we would immediately try to reopen the
temporary overlay even though the file is already unlinked.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -1163,13 +1163,6 @@ static int bdrv_open_flags(BlockDriverState *bs, int flags)
      */
     open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_PROTOCOL);
 
-    /*
-     * Snapshots should be writable.
-     */
-    if (flags & BDRV_O_TEMPORARY) {
-        open_flags |= BDRV_O_RDWR;
-    }
-
     return open_flags;
 }
 

tests/qemu-iotests/051

@@ -356,6 +356,13 @@ $QEMU_IO -c "read -P 0x33 0 4k" "$TEST_IMG" | _filter_qemu_io
 # Using snapshot=on with a non-existent TMPDIR
 TMPDIR=/nonexistent run_qemu -drive driver=null-co,snapshot=on
 
+# Using snapshot=on together with read-only=on
+echo "info block" |
+    run_qemu -drive file="$TEST_IMG",snapshot=on,read-only=on,if=none,id=$device_id |
+    _filter_qemu_io |
+    sed -e 's#"/[^"]*/vl\.[A-Za-z0-9]\{6\}"#SNAPSHOT_PATH#g'
+
+
 # success, all done
 echo "*** done"
 rm -f $seq.full

tests/qemu-iotests/051.out

@@ -458,4 +458,13 @@ read 4096/4096 bytes at offset 0
 Testing: -drive driver=null-co,snapshot=on
 QEMU_PROG: -drive driver=null-co,snapshot=on: Could not get temporary filename: No such file or directory
 
+Testing: -drive file=TEST_DIR/t.qcow2,snapshot=on,read-only=on,if=none,id=drive0
+QEMU X.Y.Z monitor - type 'help' for more information
+(qemu) info block
+drive0 (NODE_NAME): json:{"backing": {"driver": "qcow2", "file": {"driver": "file", "filename": "TEST_DIR/t.qcow2"}}, "driver": "qcow2", "file": {"driver": "file", "filename": SNAPSHOT_PATH}} (qcow2, read-only)
+    Removable device: not locked, tray closed
+    Cache mode:       writeback, ignore flushes
+    Backing file:     TEST_DIR/t.qcow2 (chain depth: 1)
+(qemu) quit
+
 *** done

tests/qemu-iotests/051.pc.out

@@ -530,4 +530,13 @@ read 4096/4096 bytes at offset 0
 Testing: -drive driver=null-co,snapshot=on
 QEMU_PROG: -drive driver=null-co,snapshot=on: Could not get temporary filename: No such file or directory
 
+Testing: -drive file=TEST_DIR/t.qcow2,snapshot=on,read-only=on,if=none,id=drive0
+QEMU X.Y.Z monitor - type 'help' for more information
+(qemu) info block
+drive0 (NODE_NAME): json:{"backing": {"driver": "qcow2", "file": {"driver": "file", "filename": "TEST_DIR/t.qcow2"}}, "driver": "qcow2", "file": {"driver": "file", "filename": SNAPSHOT_PATH}} (qcow2, read-only)
+    Removable device: not locked, tray closed
+    Cache mode:       writeback, ignore flushes
+    Backing file:     TEST_DIR/t.qcow2 (chain depth: 1)
+(qemu) quit
+
 *** done