On 09/07/2012 10:45 AM, Sage Weil wrote:
> On Thu, 6 Sep 2012, Alex Elder wrote:
>> Add the ability to map an rbd image read-only, by specifying either
>> "read_only" or "ro" as an option on the rbd "command line." Also
>> allow the inverse to be explicitly specified using "read_write" or
>> "rw".
>>
>> Signed-off-by: Alex Elder <elder@xxxxxxxxxxx>
>> ---
>> v2: - Made the read_only/ro flag explicitly make the mapping
>> read-only rather than having it toggle.
>> - Added read_write/rw flags to allow a writable mapping to
>> be explicitly requested. Snapshot mappings are silently
>> mapped read-only (even if read_write was requested).
>
> If rw is the default, and rw is silently ignored if the image itself is a
> snapshot, what is the value in rw? Would it make more sense to fail with
> EROFS if you specify rw on a snapshot (or otherwise read-only image)?
I explicitly called this out because what I wanted to do was simply too
hard.
Namely:
- default for base image map would be read-write
- default for snapshot map would be read-only
- attempt to map snapshot read-write would be met with a "ignoring"
warning
But the way the argument parsing is structured, you never have all the
information you want at the right time to do the above. So I punted
and just decided attempts to read-write map a snapshot would be silently
ignored.
I'll take a look at simply failing on a read-write mount of a snapshot
and if it's workable I'll do that.
-Alex
PS As I told to Josh separately, one of the reasons I even put in the
read-only option in the first place is to have a reason to preserve
the argument parsing infrastructure. And that's why it gets added
at this position in the series--so that code remains after the next
patch, which removes the only other option (notify_timeout). But it
also seemed like a (marginally) useful option either way.
> sage
>
>>
>> drivers/block/rbd.c | 28 ++++++++++++++++++++++++----
>> 1 file changed, 24 insertions(+), 4 deletions(-)
>>
>> Index: b/drivers/block/rbd.c
>> ===================================================================
>> --- a/drivers/block/rbd.c
>> +++ b/drivers/block/rbd.c
>> @@ -69,7 +69,8 @@
>> #define DEV_NAME_LEN 32
>> #define MAX_INT_FORMAT_WIDTH ((5 * sizeof (int)) / 2 + 1)
>>
>> -#define RBD_NOTIFY_TIMEOUT_DEFAULT 10
>> +#define RBD_NOTIFY_TIMEOUT_DEFAULT 10
>> +#define RBD_READ_ONLY_DEFAULT false
>>
>> /*
>> * block device image metadata (in-memory version)
>> @@ -91,6 +92,7 @@ struct rbd_image_header {
>>
>> struct rbd_options {
>> int notify_timeout;
>> + bool read_only;
>> };
>>
>> /*
>> @@ -176,7 +178,7 @@ struct rbd_device {
>> u64 snap_id; /* current snapshot id */
>> /* whether the snap_id this device reads from still exists */
>> bool snap_exists;
>> - int read_only;
>> + bool read_only;
>>
>> struct list_head node;
>>
>> @@ -351,12 +353,21 @@ enum {
>> /* int args above */
>> Opt_last_string,
>> /* string args above */
>> + Opt_read_only,
>> + Opt_read_write,
>> + /* Boolean args above */
>> + Opt_last_bool,
>> };
>>
>> static match_table_t rbd_opts_tokens = {
>> {Opt_notify_timeout, "notify_timeout=%d"},
>> /* int args above */
>> /* string args above */
>> + {Opt_read_only, "read_only"},
>> + {Opt_read_only, "ro"}, /* Alternate spelling */
>> + {Opt_read_write, "read_write"},
>> + {Opt_read_write, "rw"}, /* Alternate spelling */
>> + /* Boolean args above */
>> {-1, NULL}
>> };
>>
>> @@ -381,6 +392,8 @@ static int parse_rbd_opts_token(char *c,
>> } else if (token > Opt_last_int && token < Opt_last_string) {
>> dout("got string token %d val %s\n", token,
>> argstr[0].from);
>> + } else if (token > Opt_last_string && token < Opt_last_bool) {
>> + dout("got Boolean token %d\n", token);
>> } else {
>> dout("got token %d\n", token);
>> }
>> @@ -389,6 +402,12 @@ static int parse_rbd_opts_token(char *c,
>> case Opt_notify_timeout:
>> rbd_opts->notify_timeout = intval;
>> break;
>> + case Opt_read_only:
>> + rbd_opts->read_only = true;
>> + break;
>> + case Opt_read_write:
>> + rbd_opts->read_only = false;
>> + break;
>> default:
>> BUG_ON(token);
>> }
>> @@ -407,6 +426,7 @@ static int rbd_get_client(struct rbd_dev
>> struct rbd_client *rbdc;
>>
>> rbd_opts->notify_timeout = RBD_NOTIFY_TIMEOUT_DEFAULT;
>> + rbd_opts->read_only = RBD_READ_ONLY_DEFAULT;
>>
>> ceph_opts = ceph_parse_options(options, mon_addr,
>> mon_addr + mon_addr_len,
>> @@ -620,7 +640,7 @@ static int rbd_header_set_snap(struct rb
>> sizeof (RBD_SNAP_HEAD_NAME))) {
>> rbd_dev->snap_id = CEPH_NOSNAP;
>> rbd_dev->snap_exists = false;
>> - rbd_dev->read_only = 0;
>> + rbd_dev->read_only = rbd_dev->rbd_opts.read_only;
>> if (size)
>> *size = rbd_dev->header.image_size;
>> } else {
>> @@ -632,7 +652,7 @@ static int rbd_header_set_snap(struct rb
>> goto done;
>> rbd_dev->snap_id = snap_id;
>> rbd_dev->snap_exists = true;
>> - rbd_dev->read_only = 1;
>> + rbd_dev->read_only = true; /* No choice for snapshots */
>> }
>>
>> ret = 0;
>> --
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>>
>
>
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