Re: [PATCH 1/7] rbd: separate mapping info in rbd_dev

[Alex Elder <elder@inktank.com>]

On 09/07/2012 01:58 PM, Josh Durgin wrote:
> Might want to keep the comments about the fields
> moved to the mapping struct, but it looks good to me.
> 
> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

I'm going to leave this as-is.  I'm going to definitely be
reworking all these structures in the coming weeks to more
clearly separate images from snapshots, and I'll try to
improve how things are documented as I go.

					-Alex

> On 09/07/2012 06:45 AM, Alex Elder wrote:
>> Several fields in a struct rbd_dev are related to what is mapped, as
>> opposed to the actual base rbd image.  If the base image is mapped
>> these are almost unneeded, but if a snapshot is mapped they describe
>> information about that snapshot.
>>
>> In some contexts this can be a little bit confusing.  So group these
>> mapping-related field into a structure to make it clear what they
>> are describing.
>>
>> This also includes a minor change that rearranges the fields in the
>> in-core image header structure so that invariant fields are at the
>> top, followed by those that change.
>>
>> Signed-off-by: Alex Elder <elder@inktank.com>
>> ---
>>   drivers/block/rbd.c |   83
>> ++++++++++++++++++++++++++++-----------------------
>>   1 file changed, 45 insertions(+), 38 deletions(-)
>>
>> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
>> index eb6b772..dff6210 100644
>> --- a/drivers/block/rbd.c
>> +++ b/drivers/block/rbd.c
>> @@ -81,13 +81,15 @@
>>    * block device image metadata (in-memory version)
>>    */
>>   struct rbd_image_header {
>> -    u64 image_size;
>> +    /* These four fields never change for a given rbd image */
>>       char *object_prefix;
>>       __u8 obj_order;
>>       __u8 crypt_type;
>>       __u8 comp_type;
>> -    struct ceph_snap_context *snapc;
>>
>> +    /* The remaining fields need to be updated occasionally */
>> +    u64 image_size;
>> +    struct ceph_snap_context *snapc;
>>       char *snap_names;
>>       u64 *snap_sizes;
>>
>> @@ -146,6 +148,13 @@ struct rbd_snap {
>>       u64            id;
>>   };
>>
>> +struct rbd_mapping {
>> +    char                    *snap_name;
>> +    u64                     snap_id;
>> +    bool                    snap_exists;
>> +    bool            read_only;
>> +};
>> +
>>   /*
>>    * a single device
>>    */
>> @@ -174,13 +183,8 @@ struct rbd_device {
>>
>>       /* protects updating the header */
>>       struct rw_semaphore     header_rwsem;
>> -    /* name of the snapshot this device reads from */
>> -    char                    *snap_name;
>> -    /* id of the snapshot this device reads from */
>> -    u64                     snap_id;    /* current snapshot id */
>> -    /* whether the snap_id this device reads from still exists */
>> -    bool                    snap_exists;
>> -    bool            read_only;
>> +
>> +    struct rbd_mapping    mapping;
>>
>>       struct list_head    node;
>>
>> @@ -261,11 +265,11 @@ static int rbd_open(struct block_device *bdev,
>> fmode_t mode)
>>   {
>>       struct rbd_device *rbd_dev = bdev->bd_disk->private_data;
>>
>> -    if ((mode & FMODE_WRITE) && rbd_dev->read_only)
>> +    if ((mode & FMODE_WRITE) && rbd_dev->mapping.read_only)
>>           return -EROFS;
>>
>>       rbd_get_dev(rbd_dev);
>> -    set_device_ro(bdev, rbd_dev->read_only);
>> +    set_device_ro(bdev, rbd_dev->mapping.read_only);
>>
>>       return 0;
>>   }
>> @@ -375,7 +379,7 @@ enum {
>>   static match_table_t rbd_opts_tokens = {
>>       /* int args above */
>>       /* string args above */
>> -    {Opt_read_only, "read_only"},
>> +    {Opt_read_only, "mapping.read_only"},
>>       {Opt_read_only, "ro"},        /* Alternate spelling */
>>       {Opt_read_write, "read_write"},
>>       {Opt_read_write, "rw"},        /* Alternate spelling */
>> @@ -583,13 +587,13 @@ static int rbd_header_from_disk(struct
>> rbd_image_header *header,
>>           header->snap_sizes = NULL;
>>       }
>>
>> -    header->image_size = le64_to_cpu(ondisk->image_size);
>>       header->obj_order = ondisk->options.order;
>>       header->crypt_type = ondisk->options.crypt_type;
>>       header->comp_type = ondisk->options.comp_type;
>>
>>       /* Allocate and fill in the snapshot context */
>>
>> +    header->image_size = le64_to_cpu(ondisk->image_size);
>>       size = sizeof (struct ceph_snap_context);
>>       size += snap_count * sizeof (header->snapc->snaps[0]);
>>       header->snapc = kzalloc(size, GFP_KERNEL);
>> @@ -645,23 +649,24 @@ static int rbd_header_set_snap(struct rbd_device
>> *rbd_dev, u64 *size)
>>
>>       down_write(&rbd_dev->header_rwsem);
>>
>> -    if (!memcmp(rbd_dev->snap_name, RBD_SNAP_HEAD_NAME,
>> +    if (!memcmp(rbd_dev->mapping.snap_name, RBD_SNAP_HEAD_NAME,
>>               sizeof (RBD_SNAP_HEAD_NAME))) {
>> -        rbd_dev->snap_id = CEPH_NOSNAP;
>> -        rbd_dev->snap_exists = false;
>> -        rbd_dev->read_only = rbd_dev->rbd_opts.read_only;
>> +        rbd_dev->mapping.snap_id = CEPH_NOSNAP;
>> +        rbd_dev->mapping.snap_exists = false;
>> +        rbd_dev->mapping.read_only = rbd_dev->rbd_opts.read_only;
>>           if (size)
>>               *size = rbd_dev->header.image_size;
>>       } else {
>>           u64 snap_id = 0;
>>
>> -        ret = snap_by_name(&rbd_dev->header, rbd_dev->snap_name,
>> +        ret = snap_by_name(&rbd_dev->header,
>> +                    rbd_dev->mapping.snap_name,
>>                       &snap_id, size);
>>           if (ret < 0)
>>               goto done;
>> -        rbd_dev->snap_id = snap_id;
>> -        rbd_dev->snap_exists = true;
>> -        rbd_dev->read_only = true;    /* No choice for snapshots */
>> +        rbd_dev->mapping.snap_id = snap_id;
>> +        rbd_dev->mapping.snap_exists = true;
>> +        rbd_dev->mapping.read_only = true;
>>       }
>>
>>       ret = 0;
>> @@ -1532,7 +1537,7 @@ static void rbd_rq_fn(struct request_queue *q)
>>           size = blk_rq_bytes(rq);
>>           ofs = blk_rq_pos(rq) * SECTOR_SIZE;
>>           rq_bio = rq->bio;
>> -        if (do_write && rbd_dev->read_only) {
>> +        if (do_write && rbd_dev->mapping.read_only) {
>>               __blk_end_request_all(rq, -EROFS);
>>               continue;
>>           }
>> @@ -1541,7 +1546,8 @@ static void rbd_rq_fn(struct request_queue *q)
>>
>>           down_read(&rbd_dev->header_rwsem);
>>
>> -        if (rbd_dev->snap_id != CEPH_NOSNAP && !rbd_dev->snap_exists) {
>> +        if (rbd_dev->mapping.snap_id != CEPH_NOSNAP &&
>> +                !rbd_dev->mapping.snap_exists) {
>>               up_read(&rbd_dev->header_rwsem);
>>               dout("request for non-existent snapshot");
>>               spin_lock_irq(q->queue_lock);
>> @@ -1595,7 +1601,7 @@ static void rbd_rq_fn(struct request_queue *q)
>>                             coll, cur_seg);
>>               else
>>                   rbd_req_read(rq, rbd_dev,
>> -                         rbd_dev->snap_id,
>> +                         rbd_dev->mapping.snap_id,
>>                            ofs,
>>                            op_size, bio,
>>                            coll, cur_seg);
>> @@ -1767,7 +1773,7 @@ static int rbd_header_add_snap(struct rbd_device
>> *rbd_dev,
>>       struct ceph_mon_client *monc;
>>
>>       /* we should create a snapshot only if we're pointing at the
>> head */
>> -    if (rbd_dev->snap_id != CEPH_NOSNAP)
>> +    if (rbd_dev->mapping.snap_id != CEPH_NOSNAP)
>>           return -EINVAL;
>>
>>       monc = &rbd_dev->rbd_client->client->monc;
>> @@ -1821,7 +1827,7 @@ static int __rbd_refresh_header(struct rbd_device
>> *rbd_dev, u64 *hver)
>>       down_write(&rbd_dev->header_rwsem);
>>
>>       /* resized? */
>> -    if (rbd_dev->snap_id == CEPH_NOSNAP) {
>> +    if (rbd_dev->mapping.snap_id == CEPH_NOSNAP) {
>>           sector_t size = (sector_t) h.image_size / SECTOR_SIZE;
>>
>>           dout("setting size to %llu sectors", (unsigned long long)
>> size);
>> @@ -2004,7 +2010,7 @@ static ssize_t rbd_snap_show(struct device *dev,
>>   {
>>       struct rbd_device *rbd_dev = dev_to_rbd_dev(dev);
>>
>> -    return sprintf(buf, "%s\n", rbd_dev->snap_name);
>> +    return sprintf(buf, "%s\n", rbd_dev->mapping.snap_name);
>>   }
>>
>>   static ssize_t rbd_image_refresh(struct device *dev,
>> @@ -2205,11 +2211,12 @@ static int rbd_dev_snap_devs_update(struct
>> rbd_device *rbd_dev)
>>
>>               /* Existing snapshot not in the new snap context */
>>
>> -            if (rbd_dev->snap_id == snap->id)
>> -                rbd_dev->snap_exists = false;
>> +            if (rbd_dev->mapping.snap_id == snap->id)
>> +                rbd_dev->mapping.snap_exists = false;
>>               __rbd_remove_snap_dev(snap);
>>               dout("%ssnap id %llu has been removed\n",
>> -                rbd_dev->snap_id == snap->id ? "mapped " : "",
>> +                rbd_dev->mapping.snap_id == snap->id ?
>> +                                "mapped " : "",
>>                   (unsigned long long) snap->id);
>>
>>               /* Done with this list entry; advance */
>> @@ -2522,18 +2529,18 @@ static int rbd_add_parse_args(struct rbd_device
>> *rbd_dev,
>>        * The snapshot name is optional.  If none is is supplied,
>>        * we use the default value.
>>        */
>> -    rbd_dev->snap_name = dup_token(&buf, &len);
>> -    if (!rbd_dev->snap_name)
>> +    rbd_dev->mapping.snap_name = dup_token(&buf, &len);
>> +    if (!rbd_dev->mapping.snap_name)
>>           goto out_err;
>>       if (!len) {
>>           /* Replace the empty name with the default */
>> -        kfree(rbd_dev->snap_name);
>> -        rbd_dev->snap_name
>> +        kfree(rbd_dev->mapping.snap_name);
>> +        rbd_dev->mapping.snap_name
>>               = kmalloc(sizeof (RBD_SNAP_HEAD_NAME), GFP_KERNEL);
>> -        if (!rbd_dev->snap_name)
>> +        if (!rbd_dev->mapping.snap_name)
>>               goto out_err;
>>
>> -        memcpy(rbd_dev->snap_name, RBD_SNAP_HEAD_NAME,
>> +        memcpy(rbd_dev->mapping.snap_name, RBD_SNAP_HEAD_NAME,
>>               sizeof (RBD_SNAP_HEAD_NAME));
>>       }
>>
>> @@ -2642,7 +2649,7 @@ err_out_client:
>>       rbd_put_client(rbd_dev);
>>   err_put_id:
>>       if (rbd_dev->pool_name) {
>> -        kfree(rbd_dev->snap_name);
>> +        kfree(rbd_dev->mapping.snap_name);
>>           kfree(rbd_dev->header_name);
>>           kfree(rbd_dev->image_name);
>>           kfree(rbd_dev->pool_name);
>> @@ -2695,7 +2702,7 @@ static void rbd_dev_release(struct device *dev)
>>       unregister_blkdev(rbd_dev->major, rbd_dev->name);
>>
>>       /* done with the id, and with the rbd_dev */
>> -    kfree(rbd_dev->snap_name);
>> +    kfree(rbd_dev->mapping.snap_name);
>>       kfree(rbd_dev->header_name);
>>       kfree(rbd_dev->pool_name);
>>       kfree(rbd_dev->image_name);
>>
> 
> 
>