[Qemu-devel] [PATCH v2 5/8] file-posix: Support auto-read-only option

[Kevin Wolf <kwolf@redhat.com>]

If read-only=off, but auto-read-only=on is given, open the file
read-write if we have the permissions, but instead of erroring out for
read-only files, just degrade to read-only.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/file-posix.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/block/file-posix.c b/block/file-posix.c
index 2da3a76355..eead3f2df3 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -527,6 +527,19 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
 
     s->fd = -1;
     fd = qemu_open(filename, s->open_flags, 0644);
+
+    if (fd < 0 && (errno == EACCES || errno == EROFS)) {
+        /* Try to degrade to read-only, but if it doesn't work, still use the
+         * normal error message. */
+        ret = bdrv_apply_auto_read_only(bs, NULL, NULL);
+        if (ret == 0) {
+            bdrv_flags &= ~BDRV_O_RDWR;
+            raw_parse_flags(bdrv_flags, &s->open_flags);
+            assert(!(s->open_flags & O_CREAT));
+            fd = qemu_open(filename, s->open_flags);
+        }
+    }
+
     if (fd < 0) {
         ret = -errno;
         error_setg_errno(errp, errno, "Could not open '%s'", filename);
-- 
2.19.1