file-posix: Support auto-read-only option
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>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/block/file-posix.c b/block/file-posix.c
index 2da3a76..0c1b81c 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -527,9 +527,22 @@
s->fd = -1;
fd = qemu_open(filename, s->open_flags, 0644);
- if (fd < 0) {
- ret = -errno;
- error_setg_errno(errp, errno, "Could not open '%s'", filename);
+ ret = fd < 0 ? -errno : 0;
+
+ if (ret == -EACCES || ret == -EROFS) {
+ /* Try to degrade to read-only, but if it doesn't work, still use the
+ * normal error message. */
+ if (bdrv_apply_auto_read_only(bs, NULL, NULL) == 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);
+ ret = fd < 0 ? -errno : 0;
+ }
+ }
+
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "Could not open '%s'", filename);
if (ret == -EROFS) {
ret = -EACCES;
}
