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Remove two unnecessary sleeps from the hot path in bpf(4).

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The first one never triggers because bpf_canfreebuf() can only be true for
zero-copy buffers and zero-copy buffers are not read with read(2).

The second also never triggers, because we check the free buffer before
calling ROTATE_BUFFERS().  If the hold buffer is in use the free buffer
will be NULL and there is nothing else to do besides drop the packet.  If
the free buffer isn't NULL the hold buffer _is_ free and it is safe to
rotate the buffers.

Update the comment in ROTATE_BUFFERS macro to match the logic described
here.

While here fix a few typos in comments.

MFC after:	2 weeks
Sponsored by:	Rubicon Communications (Netgate)
This commit is contained in:
Luiz Otavio O Souza 2015-07-31 21:43:27 +00:00
parent faa693cdbe
commit f87e372ef2
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=286142
2 changed files with 5 additions and 11 deletions
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10
sys/net/bpf.c
View File

@ -620,7 +620,7 @@ bpf_attachd(struct bpf_d *d, struct bpf_if *bp)
bpf_detachd_locked(d);
/*
* Point d at bp, and add d to the interface's list.
* Since there are many applicaiotns using BPF for
* Since there are many applications using BPF for
* sending raw packets only (dhcpd, cdpd are good examples)
* we can delay adding d to the list of active listeners until
* some filter is configured.
@ -718,7 +718,7 @@ bpf_check_upgrade(u_long cmd, struct bpf_d *d, struct bpf_insn *fcode, int flen)
/*
* Add d to the list of active bp filters.
* Reuqires bpf_attachd() to be called before
* Requires bpf_attachd() to be called before.
*/
static void
bpf_upgraded(struct bpf_d *d)
@ -2370,9 +2370,6 @@ catchpacket(struct bpf_d *d, u_char *pkt, u_int pktlen, u_int snaplen,
* spot to do it.
*/
if (d->bd_fbuf == NULL && bpf_canfreebuf(d)) {
while (d->bd_hbuf_in_use)
mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock,
PRINET, "bd_hbuf", 0);
d->bd_fbuf = d->bd_hbuf;
d->bd_hbuf = NULL;
d->bd_hlen = 0;
@ -2415,9 +2412,6 @@ catchpacket(struct bpf_d *d, u_char *pkt, u_int pktlen, u_int snaplen,
++d->bd_dcount;
return;
}
while (d->bd_hbuf_in_use)
mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock,
PRINET, "bd_hbuf", 0);
ROTATE_BUFFERS(d);
do_wakeup = 1;
curlen = 0;

6
sys/net/bpf.h
View File

@ -1436,9 +1436,9 @@ SYSCTL_DECL(_net_bpf);
/*
* Rotate the packet buffers in descriptor d. Move the store buffer into the
* hold slot, and the free buffer ino the store slot. Zero the length of the
* new store buffer. Descriptor lock should be held. Hold buffer must
* not be marked "in use".
* hold slot, and the free buffer into the store slot. Zero the length of the
* new store buffer. Descriptor lock should be held. One must be careful to
* not rotate the buffers twice, i.e. if fbuf != NULL.
*/
#define ROTATE_BUFFERS(d) do { \
(d)->bd_hbuf = (d)->bd_sbuf; \