Commit Graph

133 Commits

Author SHA1 Message Date
Bosko Milekic
01e9ccbd9c Back out just a portion of Alfred's last commit. Remove the MBUF_CHECK
(WITNESS) for code paths that always call uma_zalloc_arg() shortly
after where the check was, because uma_zalloc_arg() already does
a similar check.

No objections from Alfred.  Thanks Alfred.
2004-07-21 21:03:01 +00:00
Alfred Perlstein
063d811465 Make sure we don't call mbuf allocation functions with mutexes held.
Discussed with: rwatson
2004-07-21 07:12:24 +00:00
Bosko Milekic
96e124135b Gah! Plug a mbuf leak I introduced in the last commit.
I don the pointy-hat.

Problem reported by: Peter Holm <pho@>
2004-06-11 18:17:25 +00:00
Bosko Milekic
b5b2ea9a46 Plug a race where upon free this scenario could occur:
(time grows downward)
thread 1         thread 2
------------|------------
dec ref_cnt |
            | dec ref_cnt  <-- ref_cnt now zero
cmpset      |
free all    |
return      |
            |
alloc again,|
reuse prev  |
ref_cnt     |
            | cmpset, read
            | already freed
            | ref_cnt
------------|------------

This should fix that by performing only a single
atomic test-and-set that will serve to decrement
the ref_cnt, only if it hasn't changed since the
earlier read, otherwise it'll loop and re-read.
This forces ordering of decrements so that truly
the thread which did the LAST decrement is the
one that frees.

This is how atomic-instruction-based refcnting
should probably be handled.

Submitted by: Julian Elischer
2004-06-10 00:04:27 +00:00
Maxime Henrion
931f76ab48 Fix a panic happening when m_getm() is called with len < MCLBYTES.
Reported by:	ale
Tested by:	ale
Reviewed by:	bosko
2004-06-09 14:53:35 +00:00
Bosko Milekic
099a0e588c Bring in mbuma to replace mballoc.
mbuma is an Mbuf & Cluster allocator built on top of a number of
extensions to the UMA framework, all included herein.

Extensions to UMA worth noting:
  - Better layering between slab <-> zone caches; introduce
    Keg structure which splits off slab cache away from the
    zone structure and allows multiple zones to be stacked
    on top of a single Keg (single type of slab cache);
    perhaps we should look into defining a subset API on
    top of the Keg for special use by malloc(9),
    for example.
  - UMA_ZONE_REFCNT zones can now be added, and reference
    counters automagically allocated for them within the end
    of the associated slab structures.  uma_find_refcnt()
    does a kextract to fetch the slab struct reference from
    the underlying page, and lookup the corresponding refcnt.

mbuma things worth noting:
  - integrates mbuf & cluster allocations with extended UMA
    and provides caches for commonly-allocated items; defines
    several zones (two primary, one secondary) and two kegs.
  - change up certain code paths that always used to do:
    m_get() + m_clget() to instead just use m_getcl() and
    try to take advantage of the newly defined secondary
    Packet zone.
  - netstat(1) and systat(1) quickly hacked up to do basic
    stat reporting but additional stats work needs to be
    done once some other details within UMA have been taken
    care of and it becomes clearer to how stats will work
    within the modified framework.

From the user perspective, one implication is that the
NMBCLUSTERS compile-time option is no longer used.  The
maximum number of clusters is still capped off according
to maxusers, but it can be made unlimited by setting
the kern.ipc.nmbclusters boot-time tunable to zero.
Work should be done to write an appropriate sysctl
handler allowing dynamic tuning of kern.ipc.nmbclusters
at runtime.

Additional things worth noting/known issues (READ):
   - One report of 'ips' (ServeRAID) driver acting really
     slow in conjunction with mbuma.  Need more data.
     Latest report is that ips is equally sucking with
     and without mbuma.
   - Giant leak in NFS code sometimes occurs, can't
     reproduce but currently analyzing; brueffer is
     able to reproduce but THIS IS NOT an mbuma-specific
     problem and currently occurs even WITHOUT mbuma.
   - Issues in network locking: there is at least one
     code path in the rip code where one or more locks
     are acquired and we end up in m_prepend() with
     M_WAITOK, which causes WITNESS to whine from within
     UMA.  Current temporary solution: force all UMA
     allocations to be M_NOWAIT from within UMA for now
     to avoid deadlocks unless WITNESS is defined and we
     can determine with certainty that we're not holding
     any locks when we're M_WAITOK.
   - I've seen at least one weird socketbuffer empty-but-
     mbuf-still-attached panic.  I don't believe this
     to be related to mbuma but please keep your eyes
     open, turn on debugging, and capture crash dumps.

This change removes more code than it adds.

A paper is available detailing the change and considering
various performance issues, it was presented at BSDCan2004:
http://www.unixdaemons.com/~bmilekic/netbuf_bmilekic.pdf
Please read the paper for Future Work and implementation
details, as well as credits.

Testing and Debugging:
    rwatson,
    brueffer,
    Ketrien I. Saihr-Kesenchedra,
    ...
Reviewed by: Lots of people (for different parts)
2004-05-31 21:46:06 +00:00
Luigi Rizzo
24665342d3 constify the last argument of m_copyback. 2004-04-18 13:01:28 +00:00
Warner Losh
7f8a436ff2 Remove advertising clause from University of California Regent's license,
per letter dated July 22, 1999.

Approved by: core
2004-04-05 21:03:37 +00:00
Mike Silbersack
b711d74eaf Style fixes: don't indent variable names.
Submitted by:	bde
2004-02-05 08:29:27 +00:00
Mike Silbersack
2ccbe4b596 Style fixes
Submitted by:	bde
2004-02-04 08:14:47 +00:00
Mike Silbersack
beb699c7ba Rewrite sendfile's header support so that headers are now sent in the first
packet along with data, instead of in their own packet.  When serving files
of size (packetsize - headersize) or smaller, this will result in one less
packet crossing the network.  Quick testing with thttpd and http_load has
shown a noticeable performance improvement in this case (350 vs 330 fetches
per second.)

Included in this commit are two support routines, iov_to_uio, and m_uiotombuf;
these routines are used by sendfile to construct the header mbuf chain that
will be linked to the rest of the data in the socket buffer.
2004-02-01 07:56:44 +00:00
Mike Silbersack
8dee2f6746 Fix another 0 / NULL mixup. 2003-12-25 01:17:27 +00:00
Peter Wemm
a89ec05e3e Catch a few places where NULL (pointer) was used where 0 (integer) was
expected.
2003-12-23 02:36:43 +00:00
Bruce M Simpson
5406529771 style(9) pass and type fixups.
Submitted by:	bde
2003-12-16 14:13:47 +00:00
Bruce M Simpson
37621fd5d9 Push m_apply() and m_getptr() up into the colleciton of standard mbuf
routines, and purge them from opencrypto.

Reviewed by:	sam
Obtained from:	NetBSD
Sponsored by:	spc.org
2003-12-15 21:49:41 +00:00
Mike Silbersack
3390d47670 Implement MBUF_STRESS_TEST mark II.
Changes from the original implementation:

- Fragmentation is handled by the function m_fragment, which can
be called from whereever fragmentation is needed.  Note that this
function is wrapped in #ifdef MBUF_STRESS_TEST to discourage non-testing
use.

- m_fragment works slightly differently from the old fragmentation
code in that it allocates a seperate mbuf cluster for each fragment.
This defeats dma_map_load_mbuf/buffer's feature of coalescing adjacent
fragments.  While that is a nice feature in practice, it nerfed the
usefulness of mbuf_stress_test.

- Add two modes of random fragmentation.  Chains with fragments all of
the same random length and chains with fragments that are each uniquely
random in length may now be requested.
2003-09-01 05:55:37 +00:00
Mike Silbersack
f8bf8e397b Three fixes:
- Make m_prepend use m_gethdr instead of m_get where
  appropriate

- Make m_copym use m_gethdr instead of m_get where
  appropriate

- Add a call to m_fixhdr in m_defrag; m_defrag can't
  deal with corrupted pkthdr.len counts.

MFC after:	3 days
2003-07-19 06:03:48 +00:00
Mike Silbersack
51710a4597 Hide the m_defrag* statistics under MBUF_STRESS_TEST, there seems
to be no need to see them in the general case (and they aren't
smp-safe anyway.)

Suggested by:	hmp
MFC after:	1 week
2003-06-17 02:34:40 +00:00
David E. O'Brien
677b542ea2 Use __FBSDID(). 2003-06-11 00:56:59 +00:00
Mike Silbersack
352d050e79 Add another MBUF_STRESS_TEST feature, m_defragrandomfailures.
When enabled, this causes m_defrag to randomly return NULL (following
its normal failure case so that extra memory leaks are not introduced.)

Code similar to this was used to find / fix a few bugs last week.
2003-04-15 02:14:43 +00:00
Robert Watson
225bff6f8b Move MAC label storage for mbufs into m_tags from the m_pkthdr structure,
returning some additional room in the first mbuf in a chain, and
avoiding feature-specific contents in the mbuf header.  To do this:

- Modify mbuf_to_label() to extract the tag, returning NULL if not
  found.

- Introduce mac_init_mbuf_tag() which does most of the work
  mac_init_mbuf() used to do, except on an m_tag rather than an
  mbuf.

- Scale back mac_init_mbuf() to perform m_tag allocation and invoke
  mac_init_mbuf_tag().

- Replace mac_destroy_mbuf() with mac_destroy_mbuf_tag(), since
  m_tag's are now GC'd deep in the m_tag/mbuf code rather than
  at a higher level when mbufs are directly free()'d.

- Add mac_copy_mbuf_tag() to support m_copy_pkthdr() and related
  notions.

- Generally change all references to mbuf labels so that they use
  mbuf_to_label() rather than &mbuf->m_pkthdr.label.  This
  required no changes in the MAC policies (yay!).

- Tweak mbuf release routines to not call mac_destroy_mbuf(),
  tag destruction takes care of it for us now.

- Remove MAC magic from m_copy_pkthdr() and m_move_pkthdr() --
  the existing m_tag support does all this for us.  Note that
  we can no longer just zero the m_tag list on the target mbuf,
  rather, we have to delete the chain because m_tag's will
  already be hung off freshly allocated mbuf's.

- Tweak m_tag copying routines so that if we're copying a MAC
  m_tag, we don't do a binary copy, rather, we initialize the
  new storage and do a deep copy of the label.

- Remove use of MAC_FLAG_INITIALIZED in a few bizarre places
  having to do with mbuf header copies previously.

- When an mbuf is copied in ip_input(), we no longer need to
  explicitly copy the label because it will get handled by the
  m_tag code now.

- No longer any weird handling of MAC labels in if_loop.c during
  header copies.

- Add MPC_LOADTIME_FLAG_LABELMBUFS flag to Biba, MLS, mac_test.
  In mac_test, handle the label==NULL case, since it can be
  dynamically loaded.

In order to improve performance with this change, introduce the notion
of "lazy MAC label allocation" -- only allocate m_tag storage for MAC
labels if we're running with a policy that uses MAC labels on mbufs.
Policies declare this intent by setting the MPC_LOADTIME_FLAG_LABELMBUFS
flag in their load-time flags field during declaration.  Note: this
opens up the possibility of post-boot policy modules getting back NULL
slot entries even though they have policy invariants of non-NULL slot
entries, as the policy might have been loaded after the mbuf was
allocated, leaving the mbuf without label storage.  Policies that cannot
handle this case must be declared as NOTLATE, or must be modified.

- mac_labelmbufs holds the current cumulative status as to whether
  any policies require mbuf labeling or not.  This is updated whenever
  the active policy set changes by the function mac_policy_updateflags().
  The function iterates the list and checks whether any have the
  flag set.  Write access to this variable is protected by the policy
  list; read access is currently not protected for performance reasons.
  This might change if it causes problems.

- Add MAC_POLICY_LIST_ASSERT_EXCLUSIVE() to permit the flags update
  function to assert appropriate locks.

- This makes allocation in mac_init_mbuf() conditional on the flag.

Reviewed by:	sam
Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, Network Associates Laboratories
2003-04-14 20:39:06 +00:00
Robert Watson
aa65d9f538 Use MBTOM() to convert mbuf allocator flags to malloc() flags, rather
than using the same compare/substitute in many places.

Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, Network Associates Laboratories
2003-04-14 16:04:10 +00:00
Dag-Erling Smørgrav
fe58453891 Introduce an M_ASSERTPKTHDR() macro which performs the very common task
of asserting that an mbuf has a packet header.  Use it instead of hand-
rolled versions wherever applicable.

Submitted by:	Hiten Pandya <hiten@unixdaemons.com>
2003-04-08 14:25:47 +00:00
Mike Silbersack
55e9f80d76 Add the m_defrag routine, as discussed on committers@. This
incarnation should address the concerns of all in the discussion,
and keeps statistics which show how much it is used.

MFC after:	2 weeks
2003-03-29 05:48:36 +00:00
Mike Silbersack
df8c7fc96e Allow m_dup_pkthdr to accept mbufs with attached clusters as
targets.

Submitted by:	bmilekic
2003-03-28 05:57:48 +00:00
Ian Dowse
a80cc4e104 In m_dup_pkthdr(), convert the supplied `how' argument into malloc
flags when passing it into m_tag_copy_chain(), as m_tag* functions
use malloc, not mbuf flags.
2003-03-13 09:02:19 +00:00
Warner Losh
a163d034fa Back out M_* changes, per decision of the TRB.
Approved by: trb
2003-02-19 05:47:46 +00:00
Alfred Perlstein
44956c9863 Remove M_TRYWAIT/M_WAITOK/M_WAIT. Callers should use 0.
Merge M_NOWAIT/M_DONTWAIT into a single flag M_NOWAIT.
2003-01-21 08:56:16 +00:00
Sam Leffler
9967cafc49 Correct mbuf packet header propagation. Previously, packet headers
were sometimes propagated using M_COPY_PKTHDR which actually did
something between a "move" and a  "copy" operation.  This is replaced
by M_MOVE_PKTHDR (which copies the pkthdr contents and "removes" it
from the source mbuf) and m_dup_pkthdr which copies the packet
header contents including any m_tag chain.  This corrects numerous
problems whereby mbuf tags could be lost during packet manipulations.

These changes also introduce arguments to m_tag_copy and m_tag_copy_chain
to specify if the tag copy work should potentially block.  This
introduces an incompatibility with openbsd which we may want to revisit.

Note that move/dup of packet headers does not handle target mbufs
that have a cluster bound to them.  We may want to support this;
for now we watch for it with an assert.

Finally, M_COPYFLAGS was updated to include M_FIRSTFRAG|M_LASTFRAG.

Supported by:	Vernier Networks
Reviewed by:	Robert Watson <rwatson@FreeBSD.org>
2002-12-30 20:22:40 +00:00
Sam Leffler
5d84645305 Replace aux mbufs with packet tags:
o instead of a list of mbufs use a list of m_tag structures a la openbsd
o for netgraph et. al. extend the stock openbsd m_tag to include a 32-bit
  ABI/module number cookie
o for openbsd compatibility define a well-known cookie MTAG_ABI_COMPAT and
  use this in defining openbsd-compatible m_tag_find and m_tag_get routines
o rewrite KAME use of aux mbufs in terms of packet tags
o eliminate the most heavily used aux mbufs by adding an additional struct
  inpcb parameter to ip_output and ip6_output to allow the IPsec code to
  locate the security policy to apply to outbound packets
o bump __FreeBSD_version so code can be conditionalized
o fixup ipfilter's call to ip_output based on __FreeBSD_version

Reviewed by:	julian, luigi (silent), -arch, -net, darren
Approved by:	julian, silence from everyone else
Obtained from:	openbsd (mostly)
MFC after:	1 month
2002-10-16 01:54:46 +00:00
Julian Elischer
4a3276d4a4 While well intentionned the check to see it there is a packet
header and return that length, was misguided.

The check itself didn't take into account the fact that the
mbuf pointer pased in may be null, and the function is
defined specifically for cases where the caller knows what it wants.
Rather than fix the check I'm removing it as phk suggested.

Submitted by:	 phk@freebsd.org
2002-09-19 08:28:41 +00:00
Julian Elischer
4a49235b89 fix style.. Return in the kernel always has () around the arguments. 2002-09-19 03:18:44 +00:00
Julian Elischer
1494277d50 Compiler was correct:
m WAS being used uninitialized..
2002-09-19 03:15:39 +00:00
Darren Reed
e62497713c If M_PKTHDR is set then we don't need to do a loop to find the total length. 2002-09-19 01:21:24 +00:00
Bosko Milekic
bd395ae8f6 style nit: unsigned -> u_int in the kernel, particularly to
stay consistent in this file, and keep m_length() and m_fixhdr()
consistent with their prototypes in mbuf.h

Inspired by: bde
2002-09-18 22:33:52 +00:00
Poul-Henning Kamp
4e4425d486 Make m_length() and m_fixhdr() return unsigned.
Suggested by:	arr
2002-09-18 19:42:06 +00:00
Poul-Henning Kamp
ac6e585d24 Introduce the m_length() function which will return the accumulated
length of an mbuf-chain and optionally a pointer to the last mbuf.
2002-09-18 14:57:35 +00:00
Poul-Henning Kamp
3f2e06c5e1 Move m_fixhdr() from "mbchain" to "mbuf" where it belongs. 2002-09-18 13:41:37 +00:00
Robert Watson
f9d0d52459 Include file cleanup; mac.h and malloc.h at one point had ordering
relationship requirements, and no longer do.

Reminded by:	bde
2002-08-01 17:47:56 +00:00
Robert Watson
e32a5b94d8 Introduce support for Mandatory Access Control and extensible
kernel access control.

Invoke additional MAC entry points when an mbuf packet header is
copied to another mbuf: release the old label if any, reinitialize
the new header, and ask the MAC framework to copy the header label
data.  Note that this requires a potential allocation operation,
but m_copy_pkthdr() is not permitted to fail, so we must block.
Since we now use interrupt threads, this is possible, but not
desirable.

Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, NAI Labs
2002-07-31 01:51:34 +00:00
Robert Watson
e37b1fcdee Make M_COPY_PKTHDR() macro into a wrapper for a m_copy_pkthdr()
function.  This permits conditionally compiled extensions to the
packet header copying semantic, such as extensions to copy MAC
labels.

Reviewed by:	bmilekic
Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, NAI Labs
2002-07-30 18:28:58 +00:00
Bosko Milekic
4151d2e620 Move m_freem() from uipc_mbuf.c to subr_mbuf.c so it can take advantage
of the inlines, like its cousin, m_free().  Also, make a small (first
step?) optimisation of m_free() to use the MBP_PERSIST{,ENT} interface
to hold the lock across frees when possible.  The thing is that right
now, we can only do this easily for at most across one mbuf + one
cluster free, as the comment mentions (it also explains why).  Anyway,
some basic tests revealed a 5-10% overall improvement.  Some of the
results can be found here:
http://people.freebsd.org/~bmilekic/code/measure.txt
2002-07-24 15:11:23 +00:00
Bosko Milekic
185c2244ce o Introduce new m_getcl() interface routine that allocates an mbuf
and a cluster in one shot.
o Introduce MBP_PERSIST and MBP_PERSISTENT control bits to mb_alloc();
  MBP_PERSIST means "if you can allocate, then keep the cache lock
  held on exit," and MBP_PERSISTENT means "a cache lock is alredy held
  on entry, so allocate from the specified (already locked) cache."
  They may be used in combination.
o m_getcl() uses the MBP_PERSIST/MBP_PERSISTENT interface so that it
  doesn't drop the cache lock in between the mbuf and cluster allocations.
o m_getm(), which takes a size and allocates an mbuf + cluster "best fit"
  chain, has been moved from uipc_mbuf.c to subr_mbuf.c and shown how to
  use MBP_PERSIST/MBP_PERSISTENT to attempt to do a grouped allocation
  without dropping the cache lock in between.

Why this is good: much less bus-locked lock acquires/drops when they're
not needed.  Also, prototype for m_getcl():
struct mbuf * m_getcl(int how, short type, int flags);
"how" and "type" are self-explanatory.  "flags" may be M_PKTHDR, in
which case m_getcl() will make the mbuf a pkthdr-mbuf.

While I'm in subr_mbuf.c:
o Every exported routine now has a nice comment with a description of
  the expected arguments.  Eventually, mbuf(9) needs to be re-vamped
  but there's still more code to write/finalize before I get to that.
o internal macros have been changed a bit.
o consistently use 'short' for "type."  This somehow slipped through
  before (that 'type' was sometimes declared as int).

Alfred has been pushing for the MBP_PERSIST{,ENT} thing for almost a
year now.  Luigi asked for m_getcl(), and will probably MFC that
part of this commit.

TODO [Related]: teach mb_free() about MBP_PERSIST{, ENT}.
2002-07-15 15:32:59 +00:00
Archie Cobbs
48d183faca Fix a bug in m_split(): the "m->m_ext.ext_size" field of an mbuf was being
set to zero. This field indicates the total space in the external buffer
and therefore should not be modified after the external buffer is added.

Add a comment warning that the mbufs returned by m_split() might be read-only.

Fix M_TRAILINGSPACE() to return zero if !M_WRITABLE(m).

Reviewed by:	freebsd-net
Obtained from:	Vernier Networks, Inc.
MFC after:	1 week
2002-05-31 22:09:57 +00:00
Jeffrey Hsu
4037698769 Fix corner case where m_len was not being initialized.
Submitted by:	Maksim Yevmenkin <myevmenk@digisle.net>
MFC after:	1 week
2002-04-12 00:01:50 +00:00
Matthew Dillon
ecde8f7c29 Get rid of the twisted MFREE() macro entirely.
Reviewed by:	dg, bmilekic
MFC after:	3 days
2002-02-05 02:00:56 +00:00
David E. O'Brien
a48740b6c5 Update to C99, s/__FUNCTION__/__func__/. 2001-12-10 05:51:45 +00:00
Julian Elischer
a8cfc0ee40 Forgot to remove this un-needed test. (M_WAITOK won't fail)
I vaguely remember someone once proving it COULD return NULL..
was that changed?

Reminded by: BDE

MFC after:	2 weeks
2001-08-19 04:30:13 +00:00
Bosko Milekic
08442f8a82 Introduce numerous SMP friendly changes to the mbuf allocator. Namely,
introduce a modified allocation mechanism for mbufs and mbuf clusters; one
which can scale under SMP and which offers the possibility of resource
reclamation to be implemented in the future. Notable advantages:

 o Reduce contention for SMP by offering per-CPU pools and locks.
 o Better use of data cache due to per-CPU pools.
 o Much less code cache pollution due to excessively large allocation macros.
 o Framework for `grouping' objects from same page together so as to be able
   to possibly free wired-down pages back to the system if they are no longer
   needed by the network stacks.

 Additional things changed with this addition:

  - Moved some mbuf specific declarations and initializations from
    sys/conf/param.c into mbuf-specific code where they belong.
  - m_getclr() has been renamed to m_get_clrd() because the old name is really
    confusing. m_getclr() HAS been preserved though and is defined to the new
    name. No tree sweep has been done "to change the interface," as the old
    name will continue to be supported and is not depracated. The change was
    merely done because m_getclr() sounds too much like "m_get a cluster."
  - TEMPORARILY disabled mbtypes statistics displaying in netstat(1) and
    systat(1) (see TODO below).
  - Fixed systat(1) to display number of "free mbufs" based on new per-CPU
    stat structures.
  - Fixed netstat(1) to display new per-CPU stats based on sysctl-exported
    per-CPU stat structures. All infos are fetched via sysctl.

 TODO (in order of priority):

  - Re-enable mbtypes statistics in both netstat(1) and systat(1) after
    introducing an SMP friendly way to collect the mbtypes stats under the
    already introduced per-CPU locks (i.e. hopefully don't use atomic() - it
    seems too costly for a mere stat update, especially when other locks are
    already present).
  - Optionally have systat(1) display not only "total free mbufs" but also
    "total free mbufs per CPU pool."
  - Fix minor length-fetching issues in netstat(1) related to recently
    re-enabled option to read mbuf stats from a core file.
  - Move reference counters at least for mbuf clusters into an unused portion
    of the cluster itself, to save space and need to allocate a counter.
  - Look into introducing resource freeing possibly from a kproc.

Reviewed by (in parts): jlemon, jake, silby, terry
Tested by: jlemon (Intel & Alpha), mjacob (Intel & Alpha)
Preliminary performance measurements: jlemon (and me, obviously)
URL: http://people.freebsd.org/~bmilekic/mb_alloc/
2001-06-22 06:35:32 +00:00
Bosko Milekic
f5eece3fb9 Change m_devget()'s outdated and unused `offset' argument to actually mean
something: offset into the first mbuf of the target chain before copying
the source data over.

Make drivers using m_devget() with a first argument "data - ETHER_ALIGN"
to use the offset argument to pass ETHER_ALIGN in. The way it was previously
done is potentially dangerous if the source data was at the top of a page
and the offset caused the previous page to be copied (if the
previous page has not yet been appropriately mapped).

The old `offset' argument in m_devget() is not used anywhere (it's always
0) and dates back to ~1995 (and earlier?) when support for ethernet trailers
existed. With that support gone, it was merely collecting dust.

Tested on alpha by: jlemon
Partially submitted by: jlemon
Reviewed by: jlemon
MFC after: 3 weeks
2001-06-20 19:48:35 +00:00