The file descriptor table now allows reserving room for multiple file
descriptors without assigning their numbers. This functionality means
any error conditions happen up front and the subsequent number
assignment will never fail.
This change uses the new functionality to fix troublesome error handling
when allocating multiple file descriptors. One pty allocation error path
was even wrong.
There were subtle race conditions where one (kernel) thread may have
allocated one file descriptor, and another thread spuciously replaces it
with something else, and then the second file descriptor allocation
failed in the first thread, and it closes the first file descriptor now
pointing to a different file description. This case seems harmless but
it's not a great class of bugs to exist in the first place. The new
behavior means the file descriptions appear in the file descriptor table
without fail and never needs to be cleaned up midway and is certainly
immune to shenangians from other threads.
Reviewed-by: Pedro Falcato <pedro.falcato@gmail.com>
I hereby relicense all my work on Sortix under the ISC license as below.
All Sortix contributions by other people are already under this license,
are not substantial enough to be copyrightable, or have been removed.
All imported code from other projects is compatible with this license.
All GPL licensed code from other projects had previously been removed.
Copyright 2011-2016 Jonas 'Sortie' Termansen and contributors.
Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
