AV dislikes many parts of orangefs_devreq_writev. Besides making
orangefs_devreq_writev more easily readable and better commented,
this patch makes an effort to address some of the problems:
> The 5th is quietly ignored unless trailer_size is positive and
> status is zero. If trailer_size > 0 && status == 0, you verify that
> the length of the 5th segment is no more than trailer_size and copy
> it to vmalloc'ed buffer. Without bothering to zero the rest of that
> buffer out.
It was just wrong to allow a 5th segment that is not exactly equal to
trailer_size. Now that that's fixed, there's nothing to zero out in
the vmalloced buffer - it is exactly the right size to hold the
5th segment.
> Another API bogosity: when the 5th segment is present, successful writev()
> returns the sum of sizes of the first 4.
Added size of 5th segment to writev return...
> if concatenation of the first 4 segments is longer than
> 16 + sizeof(struct pvfs2_downcall_s) by no more than sizeof(long) => whine
> and proceed with garbage.
If 4th segment isn't exactly sizeof(struct pvfs2_downcall_s), whine and fail.
> if the 32bit value 4 bytes into op->downcall is zero and 64bit
> value following it is non-zero, the latter is interpreted as the size of
> trailer data.
The latter is what userspace claimed was the length of the trailer data.
The kernel module now compares it to the trailer iovec's iov_len as a
sanity check.
> if there's no trailer, the 5th segment (if present) is completely ignored.
Whine and fail if there should be no trailer, yet a 5th segment is present.
> if vmalloc fails, act as if status (32bit at offset 5 into
> op->downcall) had been -ENOMEM and don't look at the 5th segment at all.
whine and fail with -ENOMEM.
Signed-off-by: Mike Marshall <hubcap@omnibond.com>
