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authorAdhemerval Zanella Netto <adhemerval.zanella@linaro.org>2023-08-24 13:42:18 -0300
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2023-09-05 13:08:59 -0300
commit0d6f9f626521678f330f8bfee89e1cdb7e2b1062 (patch)
tree07f06fe07f28134c068aeeb53d1560603612a321 /NEWS
parentce2bfb856987526c2f27fb934b5eedd70d3472d7 (diff)
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posix: Add pidfd_spawn and pidfd_spawnp (BZ 30349)
Returning a pidfd allows a process to keep a race-free handle for a child process, otherwise, the caller will need to either use pidfd_open (which still might be subject to TOCTOU) or keep the old racy interface base on pid_t. To correct use pifd_spawn, the kernel must support not only returning the pidfd with clone/clone3 but also waitid (P_PIDFD) (added on Linux 5.4). If kernel does not support the waitid, pidfd return ENOSYS. It avoids the need to racy workarounds, such as reading the procfs fdinfo to get the pid to use along with other wait interfaces. These interfaces are similar to the posix_spawn and posix_spawnp, with the only difference being it returns a process file descriptor (int) instead of a process ID (pid_t). Their prototypes are: int pidfd_spawn (int *restrict pidfd, const char *restrict file, const posix_spawn_file_actions_t *restrict facts, const posix_spawnattr_t *restrict attrp, char *const argv[restrict], char *const envp[restrict]) int pidfd_spawnp (int *restrict pidfd, const char *restrict path, const posix_spawn_file_actions_t *restrict facts, const posix_spawnattr_t *restrict attrp, char *const argv[restrict_arr], char *const envp[restrict_arr]); A new symbol is used instead of a posix_spawn extension to avoid possible issues with language bindings that might track the return argument lifetime. Although on Linux pid_t and int are interchangeable, POSIX only states that pid_t should be a signed integer. Both symbols reuse the posix_spawn posix_spawn_file_actions_t and posix_spawnattr_t, to void rehash posix_spawn API or add a new one. It also means that both interfaces support the same attribute and file actions, and a new flag or file action on posix_spawn is also added automatically for pidfd_spawn. Also, using posix_spawn plumbing allows the reusing of most of the current testing with some changes: - waitid is used instead of waitpid since it is a more generic interface. - tst-posix_spawn-setsid.c is adapted to take into consideration that the caller can check for session id directly. The test now spawns itself and writes the session id as a file instead. - tst-spawn3.c need to know where pidfd_spawn is used so it keeps an extra file description unused. Checked on x86_64-linux-gnu on Linux 4.15 (no CLONE_PIDFD or waitid support), Linux 5.4 (full support), and Linux 6.2. Reviewed-by: Florian Weimer <fweimer@redhat.com>
Diffstat (limited to 'NEWS')
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diff --git a/NEWS b/NEWS
index 0b9a247..97681e6 100644
--- a/NEWS
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@@ -20,6 +20,13 @@ Major new features:
to set the cgroupv2 in the new process in a race-free manner. These
functions are GNU extensions and require a kernel with clone3 support.
+* On Linux, the pidfd_spawn and pidfd_spawp functions have been added.
+ They have a similar prototype and semantic as posix_spawn, but instead of
+ returning a process ID, they return a file descriptor that can be used
+ along other pidfd functions (like pidfd_send_signal, poll, or waitid).
+ The pidfd functionality avoids the issue of PID reuse with the traditional
+ posix_spawn interface.
+
Deprecated and removed features, and other changes affecting compatibility:
[Add deprecations, removals and changes affecting compatibility here]