Date: Mon, 21 Apr 2014 16:15:54 -0600 From: Chris Torek <torek@torek.net> To: freebsd-hackers@freebsd.org Subject: MAXPHYS in md(4) Message-ID: <201404212215.s3LMFstd045652@elf.torek.net>
next in thread | raw e-mail | index | archive | help
In svn commit: r264504 - head/sys/geom/uzip we have:
Make sure not to do I/O for more than MAXPHYS bytes. Doing so can cause
problems in our providers, such as a KASSERT in md(4). ...
That would be this one:
KASSERT(bp->bio_length <= MAXPHYS, ("bio_length %jd",
(uintmax_t)bp->bio_length));
if ((bp->bio_flags & BIO_UNMAPPED) == 0) {
pb = NULL;
aiov.iov_base = bp->bio_data;
} else {
pb = getpbuf(&md_vnode_pbuf_freecnt);
...
As it happens, the KASSERT is really only required for the
pb != NULL case, which uses one of the reserved getpbuf() buffers
that only map MAXPHYS bytes at a time. If bp->bio_flags says that
the bio is mapped, we just use the existing KVA, and VOP_READ() and
VOP_WRITE() must already break up arbitrarily large transfers.
So, it seems like the md(4) KASSERT can be moved into the "else".
Is this a good idea? (It might not help r264504 much since it
looks like r264504 wants to handle short-read results anyway, but
it seems overly restrictive to require <= MAXPHYS for the mapped
cases.)
Chris
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201404212215.s3LMFstd045652>