Re: [PATCH 8/8] man/man7/unix.7: ERRORS: Document EACCES, EAGAIN, EMSGSIZE, ENOSPC, and EPERM

["Günther Noack" <gnoack3000@gmail.com>]

Thanks for the review!

On Sat, Oct 24, 2026 at 06:03:02AM +0000, Kuniyuki Iwashima wrote:
> On Wed, 21 Oct 2026 23:08:00 +0200, Günther Noack wrote:
> > These are all returned directly from linux.git net/unix/af_unix.c:
> > 
> > EACCES
> > 	unix_find_bsd() checks path_permission(&path, MAY_WRITE) on the
> > 	socket file of the remote address.  The rule was already described
> > 	in prose, but the error was not listed.
> > 
> > EAGAIN
> > 	unix_stream_connect() returns -EAGAIN when the listener's backlog
> > 	is full and the socket is nonblocking (there is no EINPROGRESS for
> > 	AF_UNIX).  unix_dgram_sendmsg() returns -EAGAIN when the receiver's
> > 	queue is full and the send would block.
> > 
> > EMSGSIZE
> > 	unix_dgram_sendmsg() fails if 'len > sk->sk_sndbuf - 32'.  This is
> > 	the limit described in "Sockets API".
> > 
> > ENOSPC
> > 	unix_autobind() fails when all 2^20 autobind names are taken.
> > 
> > EPERM
> > 	unix_dgram_connect() and unix_dgram_sendmsg() fail if
> > 	!unix_may_send(), that is, if the target datagram socket is
> > 	connected to a socket other than the caller's.
> > 
> > 	This is not something that the remote end normally does,
> > 	but it's a possible corner case.
> > 
> > Cc: Kuniyuki Iwashima <kuniyu@google.com>
> > Assisted-by: LLM
> > Signed-off-by: Günther Noack <gnoack3000@gmail.com>
> > ---
> > 
> > Notes:
> >     Verified in code.  Kept LLM wording, which seemed OK.
> >     
> >     Remark:
> >     
> >     The case where the remote end is connected to a different socket is
> >     obscure, but still possible with Unix Domain Sockets, when a program
> >     first bind(2)s to a name, and then connect(2)s to another name.  Then
> >     that socket can be discovered by another process through the bound
> >     name, but sending a dgram fails if the sender is not the one that that
> >     socket has connected to.
> > 
> >  man/man7/unix.7 | 32 ++++++++++++++++++++++++++++++++
> >  1 file changed, 32 insertions(+)
> > 
> > diff --git a/man/man7/unix.7 b/man/man7/unix.7
> > index 054f1af75dd5..79198445c581 100644
> > --- a/man/man7/unix.7
> > +++ b/man/man7/unix.7
> > @@ -655,10 +655,25 @@ defined in
> >  .\" and it may well change, probably best not to document this now.
> >  .SH ERRORS
> >  .TP
> > +.B EACCES
> > +The caller does not have write permission on the socket file
> 
> If we align with other doc, "write permission is denied..."

Done.

(IIRC, the man pages have similar, but inconsistent, wording for this,
but this is the shorter variant.)


> > +specified as the remote address to
> > +.BR connect (2)
> > +or
> > +.BR sendto (2)
> > +(see "Pathname socket ownership and permissions", above).
> > +.TP
> >  .B EADDRINUSE
> >  The specified local address is already in use or the filesystem socket
> >  object already exists.
> 
> s/filesystem socket object/file/
> 
> Two sockets can have the same address once one's file
> is removed even without closing the socket.

Sounds good, changed it to "file"; I guess it does not matter what
kind of file is preexisting under the desired name.

–Günther