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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-24 04:52:22 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-24 04:52:22 +0000 |
commit | 3d08cd331c1adcf0d917392f7e527b3f00511748 (patch) | |
tree | 312f0d1e1632f48862f044b8bb87e602dcffb5f9 /man2/posix_fadvise.2 | |
parent | Adding debian version 6.7-2. (diff) | |
download | manpages-3d08cd331c1adcf0d917392f7e527b3f00511748.tar.xz manpages-3d08cd331c1adcf0d917392f7e527b3f00511748.zip |
Merging upstream version 6.8.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'man2/posix_fadvise.2')
-rw-r--r-- | man2/posix_fadvise.2 | 227 |
1 files changed, 0 insertions, 227 deletions
diff --git a/man2/posix_fadvise.2 b/man2/posix_fadvise.2 deleted file mode 100644 index 96c06a7..0000000 --- a/man2/posix_fadvise.2 +++ /dev/null @@ -1,227 +0,0 @@ -.\" Copyright 2003 Abhijit Menon-Sen <ams@wiw.org> -.\" and Copyright (C) 2010, 2015, 2017 Michael Kerrisk <mtk.manpages@gmail.com> -.\" -.\" SPDX-License-Identifier: Linux-man-pages-copyleft -.\" -.\" 2005-04-08 mtk, noted kernel version and added BUGS -.\" 2010-10-09, mtk, document arm_fadvise64_64() -.\" -.TH posix_fadvise 2 2023-10-31 "Linux man-pages 6.7" -.SH NAME -posix_fadvise \- predeclare an access pattern for file data -.SH LIBRARY -Standard C library -.RI ( libc ", " \-lc ) -.SH SYNOPSIS -.nf -.B #include <fcntl.h> -.P -.BI "int posix_fadvise(int " fd ", off_t " offset ", off_t " len \ -", int " advice ");" -.fi -.P -.ad l -.RS -4 -Feature Test Macro Requirements for glibc (see -.BR feature_test_macros (7)): -.RE -.P -.BR posix_fadvise (): -.nf - _POSIX_C_SOURCE >= 200112L -.fi -.SH DESCRIPTION -Programs can use -.BR posix_fadvise () -to announce an intention to access -file data in a specific pattern in the future, thus allowing the kernel -to perform appropriate optimizations. -.P -The \fIadvice\fP applies to a (not necessarily existent) region starting -at \fIoffset\fP and extending for \fIlen\fP bytes (or until the end of -the file if \fIlen\fP is 0) within the file referred to by \fIfd\fP. -The \fIadvice\fP is not binding; -it merely constitutes an expectation on behalf of -the application. -.P -Permissible values for \fIadvice\fP include: -.TP -.B POSIX_FADV_NORMAL -Indicates that the application has no advice to give about its access -pattern for the specified data. -If no advice is given for an open file, -this is the default assumption. -.TP -.B POSIX_FADV_SEQUENTIAL -The application expects to access the specified data sequentially (with -lower offsets read before higher ones). -.TP -.B POSIX_FADV_RANDOM -The specified data will be accessed in random order. -.TP -.B POSIX_FADV_NOREUSE -The specified data will be accessed only once. -.IP -Before Linux 2.6.18, \fBPOSIX_FADV_NOREUSE\fP had the -same semantics as \fBPOSIX_FADV_WILLNEED\fP. -This was probably a bug; since Linux 2.6.18, this flag is a no-op. -.TP -.B POSIX_FADV_WILLNEED -The specified data will be accessed in the near future. -.IP -\fBPOSIX_FADV_WILLNEED\fP initiates a -nonblocking read of the specified region into the page cache. -The amount of data read may be decreased by the kernel depending -on virtual memory load. -(A few megabytes will usually be fully satisfied, -and more is rarely useful.) -.TP -.B POSIX_FADV_DONTNEED -The specified data will not be accessed in the near future. -.IP -\fBPOSIX_FADV_DONTNEED\fP attempts to free cached pages associated with -the specified region. -This is useful, for example, while streaming large -files. -A program may periodically request the kernel to free cached data -that has already been used, so that more useful cached pages are not -discarded instead. -.IP -Requests to discard partial pages are ignored. -It is preferable to preserve needed data than discard unneeded data. -If the application requires that data be considered for discarding, then -.I offset -and -.I len -must be page-aligned. -.IP -The implementation -.I may -attempt to write back dirty pages in the specified region, -but this is not guaranteed. -Any unwritten dirty pages will not be freed. -If the application wishes to ensure that dirty pages will be released, -it should call -.BR fsync (2) -or -.BR fdatasync (2) -first. -.SH RETURN VALUE -On success, zero is returned. -On error, an error number is returned. -.SH ERRORS -.TP -.B EBADF -The \fIfd\fP argument was not a valid file descriptor. -.TP -.B EINVAL -An invalid value was specified for \fIadvice\fP. -.TP -.B ESPIPE -The specified file descriptor refers to a pipe or FIFO. -.RB ( ESPIPE -is the error specified by POSIX, -but before Linux 2.6.16, -.\" commit 87ba81dba431232548ce29d5d224115d0c2355ac -Linux returned -.B EINVAL -in this case.) -.SH VERSIONS -Under Linux, \fBPOSIX_FADV_NORMAL\fP sets the readahead window to the -default size for the backing device; \fBPOSIX_FADV_SEQUENTIAL\fP doubles -this size, and \fBPOSIX_FADV_RANDOM\fP disables file readahead entirely. -These changes affect the entire file, not just the specified region -(but other open file handles to the same file are unaffected). -.SS C library/kernel differences -The name of the wrapper function in the C library is -.BR posix_fadvise (). -The underlying system call is called -.BR fadvise64 () -(or, on some architectures, -.BR fadvise64_64 ()); -the difference between the two is that the former system call -assumes that the type of the \fIlen\fP argument is \fIsize_t\fP, -while the latter expects \fIloff_t\fP there. -.SS Architecture-specific variants -Some architectures require -64-bit arguments to be aligned in a suitable pair of registers (see -.BR syscall (2) -for further detail). -On such architectures, the call signature of -.BR posix_fadvise () -shown in the SYNOPSIS would force -a register to be wasted as padding between the -.I fd -and -.I offset -arguments. -Therefore, these architectures define a version of the -system call that orders the arguments suitably, -but is otherwise exactly the same as -.BR posix_fadvise (). -.P -For example, since Linux 2.6.14, ARM has the following system call: -.P -.in +4n -.EX -.BI "long arm_fadvise64_64(int " fd ", int " advice , -.BI " loff_t " offset ", loff_t " len ); -.EE -.in -.P -These architecture-specific details are generally -hidden from applications by the glibc -.BR posix_fadvise () -wrapper function, -which invokes the appropriate architecture-specific system call. -.SH STANDARDS -POSIX.1-2008. -.SH HISTORY -POSIX.1-2001. -.P -Kernel support first appeared in Linux 2.5.60; -the underlying system call is called -.BR fadvise64 (). -.\" of fadvise64_64() -Library support has been provided since glibc 2.2, -via the wrapper function -.BR posix_fadvise (). -.P -Since Linux 3.18, -.\" commit d3ac21cacc24790eb45d735769f35753f5b56ceb -support for the underlying system call is optional, -depending on the setting of the -.B CONFIG_ADVISE_SYSCALLS -configuration option. -.P -The type of the -.I len -argument was changed from -.I size_t -to -.I off_t -in POSIX.1-2001 TC1. -.SH NOTES -The contents of the kernel buffer cache can be cleared via the -.I /proc/sys/vm/drop_caches -interface described in -.BR proc (5). -.P -One can obtain a snapshot of which pages of a file are resident -in the buffer cache by opening a file, mapping it with -.BR mmap (2), -and then applying -.BR mincore (2) -to the mapping. -.SH BUGS -Before Linux 2.6.6, if -.I len -was specified as 0, then this was interpreted literally as "zero bytes", -rather than as meaning "all bytes through to the end of the file". -.SH SEE ALSO -.BR fincore (1), -.BR mincore (2), -.BR readahead (2), -.BR sync_file_range (2), -.BR posix_fallocate (3), -.BR posix_madvise (3) |