On 10/12/18 6:55 AM, Kevin Wolf wrote:
> 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);
No guarantees what errno is after this call...
> + 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);
...even though you still rely on it here.
Possible solution:
fd = qemu_open();
if (fd < 0) {
ret = -errno;
if ((errno == EACCES || errno == EROFS) &&
!bdrv_apply_auto_read_only(bs, NULL, NULL)) {
bdrv_flags ...
fd = qemu_open();
ret = fd < 0 ? -errno : 0;
}
}
if (fd < 0) {
error_setg_errno(errp, -ret, "Could not open '%s'
Another possible solution: change the contract of
bdrv_apply_auto_read_only() to leave errno unchanged (a bit odd, if the
return value is different than the incoming errno value).
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org