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authorAlex Elder <elder@inktank.com>2012-11-13 21:11:15 -0600
committerAlex Elder <elder@inktank.com>2013-01-17 15:52:03 -0600
commitc885837f7d4f8c4f5cb2a744cc6929bc078e9dc0 (patch)
tree2b4e60e8e7aee98e8f4e8c56119978160ba85cfd /Kbuild
parent7c3d22cf16f1bbcb37a73e88338c042bb49ff112 (diff)
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libceph: always allow trail in osd request
An osd request structure contains an optional trail portion, which if present will contain data to be passed in the payload portion of the message containing the request. The trail field is a ceph_pagelist pointer, and if null it indicates there is no trail. A ceph_pagelist structure contains a length field, and it can legitimately hold value 0. Make use of this to change the interpretation of the "trail" of an osd request so that every osd request has trailing data, it just might have length 0. This means we change the r_trail field in a ceph_osd_request structure from a pointer to a structure that is always initialized. Note that in ceph_osdc_start_request(), the trail pointer (or now address of that structure) is assigned to a ceph message's trail field. Here's why that's still OK (looking at net/ceph/messenger.c): - What would have resulted in a null pointer previously will now refer to a 0-length page list. That message trail pointer is used in two functions, write_partial_msg_pages() and out_msg_pos_next(). - In write_partial_msg_pages(), a null page list pointer is handled the same as a message with 0-length trail, and both result in a "in_trail" variable set to false. The trail pointer is only used if in_trail is true. - The only other place the message trail pointer is used is out_msg_pos_next(). That function is only called by write_partial_msg_pages() and only touches the trail pointer if the in_trail value it is passed is true. Therefore a null ceph_msg->trail pointer is equivalent to a non-null pointer referring to a 0-length page list structure. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
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