Linux APIs - revision history

Dank: /* Processes */

2024-05-16T21:09:46Z

Processes

← Older revision		Revision as of 21:09, 16 May 2024
Line 20:		Line 20:
	* <tt>arch_prctl(2)</tt> address architecture-specific <tt>prctl(2)</tt>-like features. It needn't generally be used. [[libc\|glibc]] provides no prototype for <tt>arch_prctl(2)</tt>.		* <tt>arch_prctl(2)</tt> address architecture-specific <tt>prctl(2)</tt>-like features. It needn't generally be used. [[libc\|glibc]] provides no prototype for <tt>arch_prctl(2)</tt>.
	** On x86-64, it supports setting and retrieving the value of the FS and GS registers.		** On x86-64, it supports setting and retrieving the value of the FS and GS registers.
			* <tt>kcmp(2)</tt> was added in 3.5 (when built with <tt>CONFIG_CHECKPOINT_RESTORE</tt>) to test whether two resources of two (possibly distinct) processes are equal. Since 5.12, this can be enabled with <tt>CONFIG_KCMP</tt>.
	===Execution resources===		===Execution resources===
	General details of cpu partitioning and affinity can be found on the [[cpuset]] page.		General details of cpu partitioning and affinity can be found on the [[cpuset]] page.

Dank: /* File descriptors */

2024-05-16T21:08:24Z

File descriptors

← Older revision		Revision as of 21:08, 16 May 2024
Line 12:		Line 12:
	* Since 2.6.22, the <tt>eventfd(2)</tt> system call returns a file descriptor that can be used for userspace and kernel to userspace event notification. It is associated with an 8-byte kernelspace counter, which the first parameter initializes. Since Linux 2.6.27, <tt>eventfd2(2)</tt> system call also accepts a ''flags'' parameter, specified using <tt>EFD_NONBLOCK</tt> and <tt>EFD_CLOEXEC</tt>. Support for <tt>eventfd(2)</tt> was added in [[Glibc\|glibc]] 2.8, and transparent support for <tt>eventfd2(2)</tt> was added in [[Glibc\|glibc]] 2.9.		* Since 2.6.22, the <tt>eventfd(2)</tt> system call returns a file descriptor that can be used for userspace and kernel to userspace event notification. It is associated with an 8-byte kernelspace counter, which the first parameter initializes. Since Linux 2.6.27, <tt>eventfd2(2)</tt> system call also accepts a ''flags'' parameter, specified using <tt>EFD_NONBLOCK</tt> and <tt>EFD_CLOEXEC</tt>. Support for <tt>eventfd(2)</tt> was added in [[Glibc\|glibc]] 2.8, and transparent support for <tt>eventfd2(2)</tt> was added in [[Glibc\|glibc]] 2.9.
	* 2.6.39 introduced <tt>name_to_handle_at()</tt> and <tt>open_by_handle_at()</tt>, similar to FreeBSD's <tt>getfh()</tt> and <tt>openfh()</tt>. They effectively break <tt>openat()</tt> into two parts.		* 2.6.39 introduced <tt>name_to_handle_at()</tt> and <tt>open_by_handle_at()</tt>, similar to FreeBSD's <tt>getfh()</tt> and <tt>openfh()</tt>. They effectively break <tt>openat()</tt> into two parts.
			* Since 6.10, <tt>fcntl(2)</tt> supports <tt>F_DUPFD_QUERY</tt> to test whether two file descriptors reference the same underlying file.

	==Synchronization==		==Synchronization==

Dank: /* File descriptors */

2024-03-11T09:01:40Z

File descriptors

← Older revision		Revision as of 09:01, 11 March 2024
Line 11:		Line 11:
	* The obsolete BSD implementation of [[asynchronous I/O]] is extended via the <tt>F_GETSIG</tt> and <tt>F_SETSIG</tt> subcommands to <tt>fcntl(2)</tt>.		* The obsolete BSD implementation of [[asynchronous I/O]] is extended via the <tt>F_GETSIG</tt> and <tt>F_SETSIG</tt> subcommands to <tt>fcntl(2)</tt>.
	* Since 2.6.22, the <tt>eventfd(2)</tt> system call returns a file descriptor that can be used for userspace and kernel to userspace event notification. It is associated with an 8-byte kernelspace counter, which the first parameter initializes. Since Linux 2.6.27, <tt>eventfd2(2)</tt> system call also accepts a ''flags'' parameter, specified using <tt>EFD_NONBLOCK</tt> and <tt>EFD_CLOEXEC</tt>. Support for <tt>eventfd(2)</tt> was added in [[Glibc\|glibc]] 2.8, and transparent support for <tt>eventfd2(2)</tt> was added in [[Glibc\|glibc]] 2.9.		* Since 2.6.22, the <tt>eventfd(2)</tt> system call returns a file descriptor that can be used for userspace and kernel to userspace event notification. It is associated with an 8-byte kernelspace counter, which the first parameter initializes. Since Linux 2.6.27, <tt>eventfd2(2)</tt> system call also accepts a ''flags'' parameter, specified using <tt>EFD_NONBLOCK</tt> and <tt>EFD_CLOEXEC</tt>. Support for <tt>eventfd(2)</tt> was added in [[Glibc\|glibc]] 2.8, and transparent support for <tt>eventfd2(2)</tt> was added in [[Glibc\|glibc]] 2.9.
			* 2.6.39 introduced <tt>name_to_handle_at()</tt> and <tt>open_by_handle_at()</tt>, similar to FreeBSD's <tt>getfh()</tt> and <tt>openfh()</tt>. They effectively break <tt>openat()</tt> into two parts.

	==Synchronization==		==Synchronization==

Dank: /* Devices */

2024-03-11T09:00:14Z

Devices

← Older revision		Revision as of 09:00, 11 March 2024
Line 82:		Line 82:
	* <tt>process_vm_readv(2)</tt> allows a process to directly read from another process's address space, while <tt>process_vm_writev(2)</tt> allows one process to write into another's. Both were introduced in 3.5, and require the CROSS_MEMORY_ATTACH kernel option.		* <tt>process_vm_readv(2)</tt> allows a process to directly read from another process's address space, while <tt>process_vm_writev(2)</tt> allows one process to write into another's. Both were introduced in 3.5, and require the CROSS_MEMORY_ATTACH kernel option.

			==Mounts==
			6.8 introduced <tt>listmount</tt> and <tt>statmount</tt>.
	==Devices==		==Devices==
	===Ethtool===		===Ethtool===
	* The <tt>SIOCETHTOOL</tt> ioctl supports low-level operations on supported networking devices. It exchanges a <tt>struct ifreq</tt> whose <tt>ifr_data</tt> field points to some ethtool struct corresponding to a provided subcommand.		* The <tt>SIOCETHTOOL</tt> ioctl supports low-level operations on supported networking devices. It exchanges a <tt>struct ifreq</tt> whose <tt>ifr_data</tt> field points to some ethtool struct corresponding to a provided subcommand.

	==See Also==		==See Also==
	* "[http://lkml.indiana.edu/hypermail/linux/kernel/0503.1/2603.html Capabilities across execve(2)]" on [[LKML]] is insightful commentary on capabilities		* "[http://lkml.indiana.edu/hypermail/linux/kernel/0503.1/2603.html Capabilities across execve(2)]" on [[LKML]] is insightful commentary on capabilities

Dank at 06:27, 5 January 2023

2023-01-05T06:27:37Z

← Older revision		Revision as of 06:27, 5 January 2023
Line 1:		Line 1:
	The Linux kernel is a protean, rapidly-changing thing. This is reflected even in "stable" APIs, especially when additions are strictly augmentative with regards to standards. Readers of classics like [[APIUE]] would do well to keep up with their [[LKML]], or at least man pages. I'm documenting departures from these standards as I come across them in various man pages and source code. The kernel man pages can be browsed at http://www.kernel.org/doc/man-pages/online_pages.html. This page serves as a companion to "[[FreeBSD APIs]]".		The Linux kernel is a protean, rapidly-changing thing. This is reflected even in "stable" APIs, especially when additions are strictly augmentative with regards to standards. Readers of classics like [[APIUE]] would do well to keep up with their [[LKML]], or at least man pages. I'm documenting departures from these standards as I come across them in various man pages and source code. The kernel man pages can be browsed at http://www.kernel.org/doc/man-pages/online_pages.html. This page serves as a companion to "[[FreeBSD APIs]]" and "[[POSIX]]".

	== File descriptors ==		== File descriptors ==

Dank: /* File descriptors */

2023-01-05T06:24:36Z

File descriptors

@@ Line 3: / Line 3: @@
 == File descriptors ==
 * Since 2.1.69 and glibc 2.1, <tt>pread(2)</tt> and <tt>pwrite(2)</tt> have allowed <tt>read(2)</tt>- and <tt>write(2)</tt>-like behavior on a file descriptor from a specified offset, without updating the offset. This allows for the atomic equivalent of an <tt>lseek(2)</tt> and an I/O, particularly useful when multiple threads are working with the same file descriptor (since file descriptor offset is shared across the process).
 * Since 2.6.23, the <tt>open(2)</tt> system call accepts the <tt>O_CLOEXEC</tt> flag (as does <tt>recvmsg(2)</tt> and the corresponding <tt>MSG_CMSG_CLOEXEC</tt> flag). This atomically sets the close-on-exec flag upon update of the dtable, protecting against a race condition arising from <tt>fork(2)</tt>+<tt>exec(2)</tt> calls in other threads.
 ** Since 2.6.24, <tt>fcntl(2)</tt> implements a <tt>F_DUPFD_CLOEXEC</tt> operation, mating <tt>O_CLOEXEC</tt> to <tt>F_DUPFD</tt>.

Dank: /* File descriptors */

2023-01-05T05:46:31Z

File descriptors

← Older revision		Revision as of 05:46, 5 January 2023
Line 2:		Line 2:

	== File descriptors ==		== File descriptors ==
			* Since 2.1.69 and glibc 2.1, <tt>pread(2)</tt> and <tt>pwrite(2)</tt> have allowed <tt>read(2)</tt>- and <tt>write(2)</tt>-like behavior on a file descriptor from a specified offset, without updating the offset. This allows for the atomic equivalent of an <tt>lseek(2)</tt> and an I/O, particularly useful when multiple threads are working with the same file descriptor (since file descriptor offset is shared across the process).
	* Since 2.6.16, the <tt>openat(2)</tt> system call can <tt>open(2)</tt> a file relative to an open directory provided as the first argument. As the man page says:		* Since 2.6.16, the <tt>openat(2)</tt> system call can <tt>open(2)</tt> a file relative to an open directory provided as the first argument. As the man page says:
	<pre> openat() and other similar system calls suffixed "at" are supported for		<pre> openat() and other similar system calls suffixed "at" are supported for

Dank: /* Memory */

2012-07-22T03:49:57Z

Memory

← Older revision		Revision as of 03:49, 22 July 2012
Line 95:		Line 95:
	* The <tt>hugetlbfs</tt> file system supports [http://www.mjmwired.net/kernel/Documentation/vm/hugetlbpage.txt reduction of mapping granularity] in the VM. It's used by (among other applications) [http://www.cyberciti.biz/tips/linux-hugetlbfs-and-mysql-performance.html MySQL] and [[kvm]]. More details are available at [[Pages]].		* The <tt>hugetlbfs</tt> file system supports [http://www.mjmwired.net/kernel/Documentation/vm/hugetlbpage.txt reduction of mapping granularity] in the VM. It's used by (among other applications) [http://www.cyberciti.biz/tips/linux-hugetlbfs-and-mysql-performance.html MySQL] and [[kvm]]. More details are available at [[Pages]].
	** The <tt>_largepages(2)/_hugepages(2)</tt> calls were present only in Linux 2.5.36-2.5.54.		** The <tt>_largepages(2)/_hugepages(2)</tt> calls were present only in Linux 2.5.36-2.5.54.
			* <tt>process_vm_readv(2)</tt> allows a process to directly read from another process's address space, while <tt>process_vm_writev(2)</tt> allows one process to write into another's. Both were introduced in 3.5, and require the CROSS_MEMORY_ATTACH kernel option.

	==Devices==		==Devices==
	===Ethtool===		===Ethtool===

Dank: /* File descriptors */ add openat

2012-05-21T07:26:00Z

File descriptors: add openat

@@ Line 2: / Line 2: @@
 == File descriptors ==
 * Since 2.6.23, the <tt>open(2)</tt> system call accepts the <tt>O_CLOEXEC</tt> flag (as does <tt>recvmsg(2)</tt> and the corresponding <tt>MSG_CMSG_CLOEXEC</tt> flag). This atomically sets the close-on-exec flag upon update of the dtable, protecting against a race condition arising from <tt>fork(2)</tt>+<tt>exec(2)</tt> calls in other threads.
 ** Since 2.6.24, <tt>fcntl(2)</tt> implements a <tt>F_DUPFD_CLOEXEC</tt> operation, mating <tt>O_CLOEXEC</tt> to <tt>F_DUPFD</tt>.
@@ Line 10: / Line 26: @@
 * The obsolete BSD implementation of [[asynchronous I/O]] is extended via the <tt>F_GETSIG</tt> and <tt>F_SETSIG</tt> subcommands to <tt>fcntl(2)</tt>.
 * Since 2.6.22, the <tt>eventfd(2)</tt> system call returns a file descriptor that can be used for userspace and kernel to userspace event notification. It is associated with an 8-byte kernelspace counter, which the first parameter initializes. Since Linux 2.6.27, <tt>eventfd2(2)</tt> system call also accepts a ''flags'' parameter, specified using <tt>EFD_NONBLOCK</tt> and <tt>EFD_CLOEXEC</tt>. Support for <tt>eventfd(2)</tt> was added in [[Glibc|glibc]] 2.8, and transparent support for <tt>eventfd2(2)</tt> was added in [[Glibc|glibc]] 2.9.
 ==Synchronization==
 * Since 2.5.7, [[Futexes|futexes]] have provided Linux's primary userspace locking primitive, and been at the heart of [[NPTL]]. Their API changed numerous times through 2.5's development.

Dank: /* Networking */

2011-12-20T21:04:05Z

Networking

← Older revision		Revision as of 21:04, 20 December 2011
Line 50:		Line 50:
	==Networking==		==Networking==
	See [[Linux APIs#Ethtool\|below]] for ethtool (SIOCETHTOOL) coverage.		See [[Linux APIs#Ethtool\|below]] for ethtool (SIOCETHTOOL) coverage.
			* <tt>recvmmsg(2)</tt>, added in 2.6.32 and [[glibc]] 2.12, allows multiple messages to be received from a socket, with a timeout, using a single system call.
			** The new flag <tt>MSG_WAITFORONE</tt> enables <tt>MSG_DONTWAIT</tt> following receipt of the first message.
			* <tt>sendmmsg(2)</tt>, added in 3.0 and [[glibc]] 2.14, allows multiple messages to be sent on a socket using a single system call.
	=== Netlink ===		=== Netlink ===
	* Kernel 2.1 introduced the Linux [[netlink]] system and the PF_NETLINK <tt>socket(2)</tt> protocol family.		* Kernel 2.1 introduced the Linux [[netlink]] system and the PF_NETLINK <tt>socket(2)</tt> protocol family.

	=== Socket Options ===		=== Socket Options ===
	====SOL_SOCKET====		====SOL_SOCKET====