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tcp: Generalise probing for tcpi_snd_wnd field

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In order to use the tcpi_snd_wnd field from the TCP_INFO getsockopt() we
need the field to be supported in the runtime kernel (snd_wnd_cap).

In fact we should check that for for every tcp_info field we want to use,
beyond the very old ones shared with BSD.  Prepare to do that, by
generalising the probing from setting a single bool to instead record the
size of the returned TCP_INFO structure.  We can then use that recorded
value to check for the presence of any field we need.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2024-10-24 15:59:21 +11:00 committed by Stefano Brivio
parent 13f0291ede
commit 81143813a6
1 changed files with 19 additions and 15 deletions
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34
tcp.c
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@ -361,10 +361,15 @@ char tcp_buf_discard [MAX_WINDOW];
/* Does the kernel support TCP_PEEK_OFF? */
bool peek_offset_cap;
/* Does the kernel report sending window in TCP_INFO (kernel commit
* 8f7baad7f035)
*/
bool snd_wnd_cap;
/* Size of data returned by TCP_INFO getsockopt() */
socklen_t tcp_info_size;
#define tcp_info_cap(f_) \
((offsetof(struct tcp_info_linux, tcpi_##f_) + \
sizeof(((struct tcp_info_linux *)NULL)->tcpi_##f_)) <= tcp_info_size)
/* Kernel reports sending window in TCP_INFO (kernel commit 8f7baad7f035) */
#define snd_wnd_cap tcp_info_cap(snd_wnd)
/* sendmsg() to socket */
static struct iovec tcp_iov [UIO_MAXIOV];
@ -2571,11 +2576,11 @@ static bool tcp_probe_peek_offset_cap(sa_family_t af)
}
/**
* tcp_probe_snd_wnd_cap() - Check if TCP_INFO reports tcpi_snd_wnd
* tcp_probe_tcp_info() - Check what data TCP_INFO reports
*
* Return: true if supported, false otherwise
* Return: Number of bytes returned by TCP_INFO getsockopt()
*/
static bool tcp_probe_snd_wnd_cap(void)
static socklen_t tcp_probe_tcp_info(void)
{
struct tcp_info_linux tinfo;
socklen_t sl = sizeof(tinfo);
@ -2595,11 +2600,7 @@ static bool tcp_probe_snd_wnd_cap(void)
close(s);
if (sl < (offsetof(struct tcp_info_linux, tcpi_snd_wnd) +
sizeof(tinfo.tcpi_snd_wnd)))
return false;
return true;
return sl;
}
/**
@ -2635,9 +2636,12 @@ int tcp_init(struct ctx *c)
(!c->ifi6 || tcp_probe_peek_offset_cap(AF_INET6));
debug("SO_PEEK_OFF%ssupported", peek_offset_cap ? " " : " not ");
snd_wnd_cap = tcp_probe_snd_wnd_cap();
debug("TCP_INFO tcpi_snd_wnd field%ssupported",
snd_wnd_cap ? " " : " not ");
tcp_info_size = tcp_probe_tcp_info();
#define dbg_tcpi(f_) debug("TCP_INFO tcpi_%s field%s supported", \
STRINGIFY(f_), tcp_info_cap(f_) ? " " : " not ")
dbg_tcpi(snd_wnd);
#undef dbg_tcpi
return 0;
}