Hello Willy,
Your commit 712f4aad406bb1 ("unix: properly account for FDs passed over
unix sockets" added accounting to ensure that the RLIMIT_NOFILE limit
could not be bypassed when passing file descriptors across UNIX
domain sockets.
Such patches should be CCed to linux-api@xxxxxxxxxxxxxxx ;-)
A documentation [atch would be great as well, but I had a shot
at cobbling some text together. Does the text below (for the unix(7)
man page) look okay?
Cheers,
Michael
ETOOMANYREFS
This error can occur for sendmsg(2) when sending a file
descriptor as ancilary data over a UNIX domain socket (see
the description of SCM_RIGHTS, above). It occurs if the
number of "in-flight" file descriptors exceeds the
RLIMIT_NOFILE resource limit and the caller does not have
the CAP_SYS_RESOURCE capability. An in-flight file
descriptor is one that has been sent using sendmsg(2) but
has not yet been accepted in the recipient process using
recvmsg(2).
This error is diagnosed since Linux 4.5. In earlier kernel
versions, it was possible to place an unlimited number of
file descriptors in flight, by sending each file descriptor
with sendmsg(2) and then closing the file descriptor so
that it was not accounted against the RLIMIT_NOFILE
resource limit.
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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