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unix.7: Fix description of abstract socket names 

As reported by Lennart Poettering:

    The part about "abstract" sockets is misleading as it suggests
    that the sockaddr returned by getsockname() would necessarily
    have the size of sizeof(struct sockaddr), which however is not
    the case: getsockname() returns exactly the sockaddr size that
    was passed in on bind(). In particular, two sockets that are
    bound to the same sockaddr but different sizes are completely
    independent.

See https://bugzilla.kernel.org/show_bug.cgi?id=19812

Reported-by: Lennart Poettering <mzxreary@0pointer.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2010-10-10 06:59:41 +02:00
parent 6074c3e6f8
commit 156a0e0d7e
1 changed files with 14 additions and 12 deletions
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26
man7/unix.7
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@ -12,7 +12,7 @@
.\" address that can appear in the sockaddr_un structure: pathname,
.\" unnamed, and abstract.
.\"
.TH UNIX 7 2010-09-10 "Linux" "Linux Programmer's Manual"
.TH UNIX 7 2010-10-10 "Linux" "Linux Programmer's Manual"
.SH NAME
unix, AF_UNIX, AF_LOCAL \- Sockets for local
interprocess communication
@ -109,24 +109,26 @@ should not be inspected.
an abstract socket address is distinguished by the fact that
.IR sun_path[0]
is a null byte ('\\0').
All of the remaining bytes in
.I sun_path
define the "name" of the socket.
The socket's address in this namespace is given by the additional
bytes in
.IR sun_path
that are covered by the specified length of the address structure.
(Null bytes in the name have no special significance.)
The name has no connection with file system pathnames.
The socket's address in this namespace is given by the rest of the
bytes in
.IR sun_path .
When the address of an abstract socket is returned by
.BR getsockname (2),
.BR getpeername (2),
and
.BR accept (2),
its length is
.IR "sizeof(struct sockaddr_un)" ,
and
.I sun_path
contains the abstract name.
the returned
.I addrlen
is greater than
.IR "sizeof(sa_family_t)"
(i.e., greater than 2), and the name of the socket is contained in
the first
.IR "(addrlen \- sizeof(sa_family_t))"
bytes of
.IR sun_path .
The abstract socket namespace is a nonportable Linux extension.
.SS Socket Options
For historical reasons these socket options are specified with a