Rich Felker
e1a51185ce
POSIX places an obscure requirement on popen which is like a limited
version of close-on-exec:
"The popen() function shall ensure that any streams from previous
popen() calls that remain open in the parent process are closed in
the new child process."
if the POSIX-future 'e' mode flag is passed, producing a pipe FILE
with FD_CLOEXEC on the underlying pipe, this requirement is
automatically satisfied. however, for applications which use multiple
concurrent popen pipes but don't request close-on-exec, fd leaks from
earlier popen calls to later ones could produce deadlock situations
where processes are waiting for a pipe EOF that will never happen.
to fix this, iterate through all open FILEs and add close actions for
those obtained from popen. this requires holding a lock on the open
file list across the posix_spawn call so that additional popen FILEs
are not created after the list is traversed. note that it's still
possible for another popen call to start and create its pipe while the
lock is held, but such pipes are created with O_CLOEXEC and only drop
close-on-exec status (when 'e' flag is omitted) under control of the
lock.
musl libc
musl, pronounced like the word "mussel", is an MIT-licensed
implementation of the standard C library targetting the Linux syscall
API, suitable for use in a wide range of deployment environments. musl
offers efficient static and dynamic linking support, lightweight code
and low runtime overhead, strong fail-safe guarantees under correct
usage, and correctness in the sense of standards conformance and
safety. musl is built on the principle that these goals are best
achieved through simple code that is easy to understand and maintain.
The 1.1 release series for musl features coverage for all interfaces
defined in ISO C99 and POSIX 2008 base, along with a number of
non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality.
For basic installation instructions, see the included INSTALL file.
Information on full musl-targeted compiler toolchains, system
bootstrapping, and Linux distributions built on musl can be found on
the project website:
http://www.musl-libc.org/