diff options
author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
---|---|---|
committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
commit | fc22b3d6507c6745911b9dfcc68f1e665ae13dbc (patch) | |
tree | ce1e3bce06471410239a6f41282e328770aa404a /upstream/fedora-rawhide/man2/pread.2 | |
parent | Initial commit. (diff) | |
download | manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.tar.xz manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.zip |
Adding upstream version 4.22.0.upstream/4.22.0
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'upstream/fedora-rawhide/man2/pread.2')
-rw-r--r-- | upstream/fedora-rawhide/man2/pread.2 | 146 |
1 files changed, 146 insertions, 0 deletions
diff --git a/upstream/fedora-rawhide/man2/pread.2 b/upstream/fedora-rawhide/man2/pread.2 new file mode 100644 index 00000000..3bfecf1e --- /dev/null +++ b/upstream/fedora-rawhide/man2/pread.2 @@ -0,0 +1,146 @@ +.\" Copyright (C) 1999 Joseph Samuel Myers. +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH pread 2 2023-10-31 "Linux man-pages 6.06" +.SH NAME +pread, pwrite \- read from or write to a file descriptor at a given offset +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <unistd.h> +.P +.BI "ssize_t pread(int " fd ", void " buf [. count "], size_t " count , +.BI " off_t " offset ); +.BI "ssize_t pwrite(int " fd ", const void " buf [. count "], size_t " count , +.BI " off_t " offset ); +.fi +.P +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.P +.BR pread (), +.BR pwrite (): +.nf + _XOPEN_SOURCE >= 500 + || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L +.fi +.SH DESCRIPTION +.BR pread () +reads up to +.I count +bytes from file descriptor +.I fd +at offset +.I offset +(from the start of the file) into the buffer starting at +.IR buf . +The file offset is not changed. +.P +.BR pwrite () +writes up to +.I count +bytes from the buffer starting at +.I buf +to the file descriptor +.I fd +at offset +.IR offset . +The file offset is not changed. +.P +The file referenced by +.I fd +must be capable of seeking. +.SH RETURN VALUE +On success, +.BR pread () +returns the number of bytes read +(a return of zero indicates end of file) +and +.BR pwrite () +returns the number of bytes written. +.P +Note that it is not an error for a successful call to transfer fewer bytes +than requested (see +.BR read (2) +and +.BR write (2)). +.P +On error, \-1 is returned and +.I errno +is set to indicate the error. +.SH ERRORS +.BR pread () +can fail and set +.I errno +to any error specified for +.BR read (2) +or +.BR lseek (2). +.BR pwrite () +can fail and set +.I errno +to any error specified for +.BR write (2) +or +.BR lseek (2). +.SH STANDARDS +POSIX.1-2008. +.SH HISTORY +POSIX.1-2001. +.P +Added in Linux 2.1.60; +the entries in the i386 system call table were added in Linux 2.1.69. +C library support (including emulation using +.BR lseek (2) +on older kernels without the system calls) was added in glibc 2.1. +.SS C library/kernel differences +On Linux, the underlying system calls were renamed +in Linux 2.6: +.BR pread () +became +.BR pread64 (), +and +.BR pwrite () +became +.BR pwrite64 (). +The system call numbers remained the same. +The glibc +.BR pread () +and +.BR pwrite () +wrapper functions transparently deal with the change. +.P +On some 32-bit architectures, +the calling signature for these system calls differ, +for the reasons described in +.BR syscall (2). +.SH NOTES +The +.BR pread () +and +.BR pwrite () +system calls are especially useful in multithreaded applications. +They allow multiple threads to perform I/O on the same file descriptor +without being affected by changes to the file offset by other threads. +.SH BUGS +POSIX requires that opening a file with the +.B O_APPEND +flag should have no effect on the location at which +.BR pwrite () +writes data. +However, on Linux, if a file is opened with +.\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=43178 +.BR O_APPEND , +.BR pwrite () +appends data to the end of the file, regardless of the value of +.IR offset . +.SH SEE ALSO +.BR lseek (2), +.BR read (2), +.BR readv (2), +.BR write (2) |