| Message ID | 1360063713-10687-1-git-send-email-stefanha@redhat.com |
|---|---|
| State | New |
| Headers | show |
Stefan Hajnoczi <stefanha@redhat.com> writes: > Linux block devices can be set read-only with "blockdev --setro > <device>". The same thing can be done for LVM volumes using "lvchange > --permission r <volume>". This read-only setting is independent of > device node permissions. Therefore the device can still be opened > O_RDWR but actual writes will fail. > > This results in odd behavior for QEMU. bdrv_open() is supposed to fail > if a read-only image is being opened with BDRV_O_RDWR. By not failing > for Linux block devices, the guest boots up but every write produces an > I/O error. > > This patch checks whether the block device is read-only so that Linux > block devices behave like regular files. > > Reported-by: Sibiao Luo <sluo@redhat.com> > Suggested-by: Paolo Bonzini <pbonzini@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Markus Armbruster <armbru@redhat.com>
Am 05.02.2013 16:12, schrieb Markus Armbruster: > Stefan Hajnoczi <stefanha@redhat.com> writes: > >> Linux block devices can be set read-only with "blockdev --setro >> <device>". The same thing can be done for LVM volumes using "lvchange >> --permission r <volume>". This read-only setting is independent of >> device node permissions. Therefore the device can still be opened >> O_RDWR but actual writes will fail. >> >> This results in odd behavior for QEMU. bdrv_open() is supposed to fail >> if a read-only image is being opened with BDRV_O_RDWR. By not failing >> for Linux block devices, the guest boots up but every write produces an >> I/O error. >> >> This patch checks whether the block device is read-only so that Linux >> block devices behave like regular files. >> >> Reported-by: Sibiao Luo <sluo@redhat.com> >> Suggested-by: Paolo Bonzini <pbonzini@redhat.com> >> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > > Reviewed-by: Markus Armbruster <armbru@redhat.com> Thanks, applied to the block branch. Kevin
diff --git a/block/raw-posix.c b/block/raw-posix.c index 8b6b926..4dfdf98 100644 --- a/block/raw-posix.c +++ b/block/raw-posix.c @@ -1257,9 +1257,43 @@ static int hdev_probe_device(const char *filename) return 0; } +static int check_hdev_writable(BDRVRawState *s) +{ +#if defined(BLKROGET) + /* Linux block devices can be configured "read-only" using blockdev(8). + * This is independent of device node permissions and therefore open(2) + * with O_RDWR succeeds. Actual writes fail with EPERM. + * + * bdrv_open() is supposed to fail if the disk is read-only. Explicitly + * check for read-only block devices so that Linux block devices behave + * properly. + */ + struct stat st; + int readonly = 0; + + if (fstat(s->fd, &st)) { + return -errno; + } + + if (!S_ISBLK(st.st_mode)) { + return 0; + } + + if (ioctl(s->fd, BLKROGET, &readonly) < 0) { + return -errno; + } + + if (readonly) { + return -EACCES; + } +#endif /* defined(BLKROGET) */ + return 0; +} + static int hdev_open(BlockDriverState *bs, const char *filename, int flags) { BDRVRawState *s = bs->opaque; + int ret; #if defined(__APPLE__) && defined(__MACH__) if (strstart(filename, "/dev/cdrom", NULL)) { @@ -1300,7 +1334,20 @@ static int hdev_open(BlockDriverState *bs, const char *filename, int flags) } #endif - return raw_open_common(bs, filename, flags, 0); + ret = raw_open_common(bs, filename, flags, 0); + if (ret < 0) { + return ret; + } + + if (flags & BDRV_O_RDWR) { + ret = check_hdev_writable(s); + if (ret < 0) { + raw_close(bs); + return ret; + } + } + + return ret; } #if defined(__linux__)
Linux block devices can be set read-only with "blockdev --setro <device>". The same thing can be done for LVM volumes using "lvchange --permission r <volume>". This read-only setting is independent of device node permissions. Therefore the device can still be opened O_RDWR but actual writes will fail. This results in odd behavior for QEMU. bdrv_open() is supposed to fail if a read-only image is being opened with BDRV_O_RDWR. By not failing for Linux block devices, the guest boots up but every write produces an I/O error. This patch checks whether the block device is read-only so that Linux block devices behave like regular files. Reported-by: Sibiao Luo <sluo@redhat.com> Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- block/raw-posix.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 48 insertions(+), 1 deletion(-)