Date: Wed, 17 Aug 2022 08:39:22 -0700 From: Gleb Smirnoff <glebius@freebsd.org> To: Mateusz Guzik <mjg@freebsd.org> Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: 9ac6eda6c6a3 - main - pipe: try to skip locking the pipe if a non-blocking fd is used Message-ID: <Yv0LqtsEbA5SB5hS@FreeBSD.org> In-Reply-To: <Yv0KfpO9i4lR9LQm@FreeBSD.org> References: <202208171423.27HENpvp024623@gitrepo.freebsd.org> <Yv0KfpO9i4lR9LQm@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Aug 17, 2022 at 08:34:22AM -0700, Gleb Smirnoff wrote:
T> This also breaks API. Although not explicitly narrated by POSIX or our
T> documentation, but there is a strong contract that, if application had
T> received a non-blocking fd from event dispatcher (kevent, poll, select)
T> as writable, then it is possible to write thre non-zero bytes with next
T> syscall.
Actually for poll(2) and kevent(2) you can almost read this contract between
the lines:
POLLWRNORM Normal data may be written without blocking.
EVFILT_WRITE Takes a descriptor as the identifier, and returns
whenever it is possible to write to the descriptor.
For sockets, pipes and fifos, data will contain the
amount of space remaining in the write buffer. The
filter will set EV_EOF when the reader disconnects,
and for the fifo case, this will be cleared when a
new reader connects. Note that this filter is not
supported for vnodes.
So with this change it may happen that previous return of poll or kevent
returned incorrect information.
--
Gleb Smirnoff
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Yv0LqtsEbA5SB5hS>