bc093719ca
The last half year I've been working on a replacement TTY layer for the FreeBSD kernel. The new TTY layer was designed to improve the following: - Improved driver model: The old TTY layer has a driver model that is not abstract enough to make it friendly to use. A good example is the output path, where the device drivers directly access the output buffers. This means that an in-kernel PPP implementation must always convert network buffers into TTY buffers. If a PPP implementation would be built on top of the new TTY layer (still needs a hooks layer, though), it would allow the PPP implementation to directly hand the data to the TTY driver. - Improved hotplugging: With the old TTY layer, it isn't entirely safe to destroy TTY's from the system. This implementation has a two-step destructing design, where the driver first abandons the TTY. After all threads have left the TTY, the TTY layer calls a routine in the driver, which can be used to free resources (unit numbers, etc). The pts(4) driver also implements this feature, which means posix_openpt() will now return PTY's that are created on the fly. - Improved performance: One of the major improvements is the per-TTY mutex, which is expected to improve scalability when compared to the old Giant locking. Another change is the unbuffered copying to userspace, which is both used on TTY device nodes and PTY masters. Upgrading should be quite straightforward. Unlike previous versions, existing kernel configuration files do not need to be changed, except when they reference device drivers that are listed in UPDATING. Obtained from: //depot/projects/mpsafetty/... Approved by: philip (ex-mentor) Discussed: on the lists, at BSDCan, at the DevSummit Sponsored by: Snow B.V., the Netherlands dcons(4) fixed by: kan
195 lines
5.9 KiB
Groff
195 lines
5.9 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getrlimit.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd August 20, 2008
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.Dt GETRLIMIT 2
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.Os
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.Sh NAME
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.Nm getrlimit ,
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.Nm setrlimit
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.Nd control maximum system resource consumption
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/time.h
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.In sys/resource.h
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.Ft int
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.Fn getrlimit "int resource" "struct rlimit *rlp"
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.Ft int
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.Fn setrlimit "int resource" "const struct rlimit *rlp"
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.Sh DESCRIPTION
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Limits on the consumption of system resources by the current process
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and each process it creates may be obtained with the
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.Fn getrlimit
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system call, and set with the
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.Fn setrlimit
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system call.
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.Pp
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The
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.Fa resource
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argument is one of the following:
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.Bl -tag -width RLIMIT_FSIZEAA
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.It Dv RLIMIT_AS
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The maximum amount (in bytes) of virtual memory the process is
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allowed to map.
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.It Dv RLIMIT_CORE
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The largest size (in bytes)
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.Xr core 5
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file that may be created.
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.It Dv RLIMIT_CPU
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The maximum amount of cpu time (in seconds) to be used by
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each process.
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.It Dv RLIMIT_DATA
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The maximum size (in bytes) of the data segment for a process;
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this defines how far a program may extend its break with the
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.Xr sbrk 2
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function.
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.It Dv RLIMIT_FSIZE
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The largest size (in bytes) file that may be created.
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.It Dv RLIMIT_MEMLOCK
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The maximum size (in bytes) which a process may lock into memory
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using the
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.Xr mlock 2
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system call.
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.It Dv RLIMIT_NOFILE
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The maximum number of open files for this process.
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.It Dv RLIMIT_NPROC
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The maximum number of simultaneous processes for this user id.
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.It Dv RLIMIT_RSS
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The maximum size (in bytes) to which a process's resident set size may
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grow.
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This imposes a limit on the amount of physical memory to be given to
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a process; if memory is tight, the system will prefer to take memory
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from processes that are exceeding their declared resident set size.
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.It Dv RLIMIT_SBSIZE
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The maximum size (in bytes) of socket buffer usage for this user.
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This limits the amount of network memory, and hence the amount of
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mbufs, that this user may hold at any time.
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.It Dv RLIMIT_STACK
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The maximum size (in bytes) of the stack segment for a process;
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this defines how far a program's stack segment may be extended.
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Stack extension is performed automatically by the system.
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.It Dv RLIMIT_NPTS
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The maximum number of pseudo-terminals created by this user id.
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.El
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.Pp
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A resource limit is specified as a soft limit and a hard limit.
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When a
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soft limit is exceeded a process may receive a signal (for example, if
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the cpu time or file size is exceeded), but it will be allowed to
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continue execution until it reaches the hard limit (or modifies
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its resource limit).
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The
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.Vt rlimit
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structure is used to specify the hard and soft limits on a resource,
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.Bd -literal -offset indent
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struct rlimit {
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rlim_t rlim_cur; /* current (soft) limit */
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rlim_t rlim_max; /* maximum value for rlim_cur */
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};
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.Ed
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.Pp
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Only the super-user may raise the maximum limits.
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Other users
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may only alter
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.Fa rlim_cur
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within the range from 0 to
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.Fa rlim_max
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or (irreversibly) lower
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.Fa rlim_max .
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.Pp
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An
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.Dq infinite
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value for a limit is defined as
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.Dv RLIM_INFINITY .
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.Pp
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Because this information is stored in the per-process information,
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this system call must be executed directly by the shell if it
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is to affect all future processes created by the shell;
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.Ic limit
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is thus a built-in command to
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.Xr csh 1 .
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.Pp
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The system refuses to extend the data or stack space when the limits
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would be exceeded in the normal way: a
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.Xr brk 2
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function fails if the data space limit is reached.
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When the stack limit is reached, the process receives
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a segmentation fault
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.Pq Dv SIGSEGV ;
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if this signal is not
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caught by a handler using the signal stack, this signal
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will kill the process.
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.Pp
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A file I/O operation that would create a file larger that the process'
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soft limit will cause the write to fail and a signal
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.Dv SIGXFSZ
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to be
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generated; this normally terminates the process, but may be caught.
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When
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the soft cpu time limit is exceeded, a signal
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.Dv SIGXCPU
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is sent to the
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offending process.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The
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.Fn getrlimit
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and
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.Fn setrlimit
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system calls
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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The address specified for
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.Fa rlp
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is invalid.
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.It Bq Er EPERM
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The limit specified to
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.Fn setrlimit
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would have
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raised the maximum limit value, and the caller is not the super-user.
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.El
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.Sh SEE ALSO
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.Xr csh 1 ,
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.Xr quota 1 ,
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.Xr quotactl 2 ,
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.Xr sigaltstack 2 ,
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.Xr sigvec 2 ,
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.Xr sysctl 3 ,
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.Xr ulimit 3
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.Sh HISTORY
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The
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.Fn getrlimit
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system call appeared in
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.Bx 4.2 .
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