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			error2 = XFS_BUF_SET_PTR(bp, offset, BBTOB(bufblks);

While at I think this mess with the buffer virtual mapping, read into it
and set it back mess needs to go into a single helper instead of beeing
duplicated three times.  By having named arguments with proper types
bugs like the existing one above should also be much more obvious to
spot.

As a follow on patch to that I think we could also get rid of all the
vmap manipultions entirely, and just specify and I/O offset and length
manually.  The only thing required for that is a number of pages
to skip at the beggining of the buffer from the log recovery code to
_xfs_buf_ioapply, either by passing it down procedurally, or by adding
a new filed to struct xfs_buf.  In fact just relaxing the b_offset
semantics to allow offsets larger than a page only in the I/O path would
do it, but I'm not sure that version helps long-term maintenance.