Pidfd - revision history

Dank: /* Glibc */

2025-01-23T08:31:47Z

Glibc

← Older revision		Revision as of 08:31, 23 January 2025
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	==[[Glibc]]==		==[[Glibc]]==
	GNU libc added pidfd system call support in 2.36. Glibc 2.39 added two functions for pidfds, complementing <tt>posix_spawn(3)</tt>. They return pidfds rather than PIDs:		GNU libc added pidfd system call support in 2.36. Glibc 2.39 added two functions for pidfds, complementing <tt>posix_spawn(3)</tt>. They return pidfds rather than PIDs:
	* <tt>pidfd_spawn(3)</tt>:analogous to <tt>posix_spawn(3)</tt>		* <tt>pidfd_spawn(3)</tt>: analogous to <tt>posix_spawn(3)</tt>
	* <tt>pidfd_spawnp(3)</tt>: analogous to <tt>posix_spawnp(3)</tt>		* <tt>pidfd_spawnp(3)</tt>: analogous to <tt>posix_spawnp(3)</tt>

Dank: /* Kernel */

2024-03-13T10:30:15Z

Kernel

← Older revision		Revision as of 10:30, 13 March 2024
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	As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.		As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.

	6.9 introduces pidfdfs, a pseudo filesystem similar to nsfs (<tt>~~/proc/PID/ns~~</tt>).		6.9 introduces pidfdfs, a pseudo filesystem similar to nsfs. This is not visible from userspace, and is not mounted. It facilitates system calls which demand a filesystem backing: <tt>statx()</tt> now works, as do LSMs (Linux Security Modules).

	==[[Glibc]]==		==[[Glibc]]==

Dank: /* See also */

2024-03-13T10:27:38Z

Dank: /* Kernel */

2024-03-13T10:27:14Z

Kernel

← Older revision		Revision as of 10:27, 13 March 2024
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	As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.		As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.

			6.9 introduces pidfdfs, a pseudo filesystem similar to nsfs (<tt>/proc/PID/ns</tt>).

	==[[Glibc]]==		==[[Glibc]]==

Dank: /* See also */

2024-02-07T03:12:48Z

Dank: /* Glibc */

2024-02-07T02:23:06Z

Glibc

← Older revision		Revision as of 02:23, 7 February 2024
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	* <tt>pidfd_spawn(3)</tt>:analogous to <tt>posix_spawn(3)</tt>		* <tt>pidfd_spawn(3)</tt>:analogous to <tt>posix_spawn(3)</tt>
	* <tt>pidfd_spawnp(3)</tt>: analogous to <tt>posix_spawnp(3)</tt>		* <tt>pidfd_spawnp(3)</tt>: analogous to <tt>posix_spawnp(3)</tt>

			The <tt>posix_spawnattr_t</tt> argument allows (among other things) spawning the process within a different control group.

	Also added was <tt>pidfd_getpid(3)</tt>:		Also added was <tt>pidfd_getpid(3)</tt>:

Dank: /* Glibc */

2024-02-07T02:21:41Z

Glibc

← Older revision		Revision as of 02:21, 7 February 2024
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	==[[Glibc]]==		==[[Glibc]]==
	GNU libc added pidfd system call support in 2.36. Glibc 2.39 added ~~several~~ functions for pidfds, complementing <tt>posix_spawn(3)</tt>:		GNU libc added pidfd system call support in 2.36. Glibc 2.39 added two functions for pidfds, complementing <tt>posix_spawn(3)</tt>. They return pidfds rather than PIDs:
	* <tt>pidfd_spawn(3)</tt>:analogous to <tt>posix_spawn(3)</tt>		* <tt>pidfd_spawn(3)</tt>:analogous to <tt>posix_spawn(3)</tt>
	* <tt>pidfd_spawnp(3)</tt>: analogous to <tt>posix_spawnp(3)</tt>		* <tt>pidfd_spawnp(3)</tt>: analogous to <tt>posix_spawnp(3)</tt>

			Also added was <tt>pidfd_getpid(3)</tt>:

	* <tt>pid_t pidfd_getpid(3)</tt>: get the PID from a pidfd		* <tt>pid_t pidfd_getpid(3)</tt>: get the PID from a pidfd

Dank at 02:20, 7 February 2024

2024-02-07T02:20:57Z

← Older revision		Revision as of 02:20, 7 February 2024
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	The first "pidfds" were created by opening a <tt>/proc/PID</tt> directory, and used with <tt>pidfd_send_signal(2)</tt>. These pidfds are now considered incomplete (they cannot be polled for process termination, nor can they be used with the <tt>waitid(2)</tt> system call).		The first "pidfds" were created by opening a <tt>/proc/PID</tt> directory, and used with <tt>pidfd_send_signal(2)</tt>. These pidfds are now considered incomplete (they cannot be polled for process termination, nor can they be used with the <tt>waitid(2)</tt> system call).

			==Kernel==
	At the heart of the modern pidfd abstraction is the <tt>CLONE_PIDFD</tt> flag to the <tt>clone(2)</tt> system call (note that this recycles the deprecated <tt>CLONE_PID</tt> bit). It is not possible to use this flag with <tt>CLONE_THREAD</tt>, and thus the created process will always be a thread group leader. It cannot be used together with the (deprecated) <tt>CLONE_DETACHED</tt> flag. The resulting file descriptor is placed in <tt>parent_tid</tt> when used with <tt>clone(2)</tt> (and thus it cannot there be used together with <tt>CLONE_PARENT_SETTID</tt>) and <tt>cl_args.pidfd</tt> when used with <tt>clone3(2)</tt>.		At the heart of the modern pidfd abstraction is the <tt>CLONE_PIDFD</tt> flag to the <tt>clone(2)</tt> system call (note that this recycles the deprecated <tt>CLONE_PID</tt> bit). It is not possible to use this flag with <tt>CLONE_THREAD</tt>, and thus the created process will always be a thread group leader. It cannot be used together with the (deprecated) <tt>CLONE_DETACHED</tt> flag. The resulting file descriptor is placed in <tt>parent_tid</tt> when used with <tt>clone(2)</tt> (and thus it cannot there be used together with <tt>CLONE_PARENT_SETTID</tt>) and <tt>cl_args.pidfd</tt> when used with <tt>clone3(2)</tt>.

	Kernel 5.3 introduced <tt>pidfd_open(2)</tt>, allowing a pidfd to be opened for an arbitrary existing process. If you for some reason can't use <tt>clone3(2)</tt>, this can be employed together with <tt>fork(2)</tt> for a race-free pidfd acquisition on children.		Kernel 5.3 introduced <tt>pidfd_open(2)</tt>, allowing a pidfd to be opened for an arbitrary existing process. If you for some reason can't use <tt>clone3(2)</tt>, this can be employed together with <tt>fork(2)</tt> for a race-free pidfd acquisition on children (see <tt>pidfd_spawn(3)</tt> below).

	Kernel 5.6 added <tt>pidfd_getfd(2)</tt>, supporting duplication of an existing file descriptor in a process identified by a pidfd. This operation requires <tt>PTRACE_MODE_ATTACH_REALCREDS</tt>.		Kernel 5.6 added <tt>pidfd_getfd(2)</tt>, supporting duplication of an existing file descriptor in a process identified by a pidfd. This operation requires <tt>PTRACE_MODE_ATTACH_REALCREDS</tt>.
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	As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.		As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.

			==[[Glibc]]==
			GNU libc added pidfd system call support in 2.36. Glibc 2.39 added several functions for pidfds, complementing <tt>posix_spawn(3)</tt>:
			* <tt>pidfd_spawn(3)</tt>:analogous to <tt>posix_spawn(3)</tt>
			* <tt>pidfd_spawnp(3)</tt>: analogous to <tt>posix_spawnp(3)</tt>
			* <tt>pid_t pidfd_getpid(3)</tt>: get the PID from a pidfd

			==See also==
			"[https://lwn.net/Articles/943022/ Race-free process creation in the GNU C library]", LWN
			"[https://lwn.net/Articles/943022/ GNU C Library version 2.39]", LWN

	[[Category: Linux]]		[[Category: Linux]]

Dank at 01:46, 1 July 2023

2023-07-01T01:46:59Z

← Older revision		Revision as of 01:46, 1 July 2023
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	As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.		As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.

			[[Category: Linux]]

Dank at 01:46, 1 July 2023

2023-07-01T01:46:42Z

← Older revision		Revision as of 01:46, 1 July 2023
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	Kernel 5.6 added <tt>pidfd_getfd(2)</tt>, supporting duplication of an existing file descriptor in a process identified by a pidfd. This operation requires <tt>PTRACE_MODE_ATTACH_REALCREDS</tt>.		Kernel 5.6 added <tt>pidfd_getfd(2)</tt>, supporting duplication of an existing file descriptor in a process identified by a pidfd. This operation requires <tt>PTRACE_MODE_ATTACH_REALCREDS</tt>.

			Kernel 5.8 added support for supplying a pidfd to <tt>setns(2)</tt>.

			Kernel 5.10 brought <tt>process_madvise(2)</tt>, generalizing <tt>madvise(2)</tt> to multiple memory regions and allowing it to be applied to another process's address space. When used on another process (as opposed to oneself), it requires <tt>PTRACE_MODE_READ_FSCREDS</tt> and <tt>CAP_SYS_NICE</tt>.

	As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.		As of 6.5, credentials can be sent using pidfds rather than <tt>SCM_CREDENTIALS</tt>-style PIDs using the <tt>SCM_PIDFD</tt> type. <tt>getsockopt(2)</tt> can use <tt>SO_PEERPIDFD</tt> to get a pidfd for the peer process on a <tt>unix(7)</tt> socket.

← Older revision		Revision as of 10:27, 13 March 2024
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	* <tt>pid_t pidfd_getpid(3)</tt>: get the PID from a pidfd		* <tt>pid_t pidfd_getpid(3)</tt>: get the PID from a pidfd

	==~~See also~~==		==External links==
	* [https://lwn.net/Articles/943022/ Race-free process creation in the GNU C library], LWN		* [https://lwn.net/Articles/943022/ Race-free process creation in the GNU C library], LWN
	* [https://lwn.net/Articles/943022/ GNU C Library version 2.39], LWN		* [https://lwn.net/Articles/943022/ GNU C Library version 2.39], LWN
			* [https://lwn.net/Articles/963749/ A new filesystem for pidfds], LWN

	[[Category: Linux]]		[[Category: Linux]]

← Older revision		Revision as of 03:12, 7 February 2024
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	==See also==		==See also==
	"[https://lwn.net/Articles/943022/ Race-free process creation in the GNU C library]", LWN		* [https://lwn.net/Articles/943022/ Race-free process creation in the GNU C library], LWN
	"[https://lwn.net/Articles/943022/ GNU C Library version 2.39]", LWN		* [https://lwn.net/Articles/943022/ GNU C Library version 2.39], LWN

	[[Category: Linux]]		[[Category: Linux]]