man2/openat.2

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  26 .TH OPENAT 2 2006-03-06 "Linux 2.6.16" "Linux Programmer's Manual"
  27 .SH NAME
  28 openat \- open a file at a relative location
  29 .SH SYNOPSIS
  30 .nf
  31 .B #include <sys/types.h>
  32 .B #include <sys/stat.h>
  33 .B #include <fcntl.h>
  34 .sp
  35 .BI "int openat(int " dirfd ", const char *" pathname ", int " flags );
  36 .BI "int openat(int " dirfd ", const char *" pathname ", int " flags \
  37 ", mode_t " mode );
  38 .fi
  39 .SH DESCRIPTION
  40 The
  41 .BR openat ()
  42 system call operates in exactly the same way as
  43 .BR open (2),
  44 except for the differences described in this manual page.
  45
  46 If the pathname given in
  47 .I pathname
  48 is relative, then it is interpreted relative to the directory
  49 referred to by the file descriptor
  50 .IR dirfd
  51 (rather than relative to the current working directory of
  52 the calling process, as is done by
  53 .BR open (2)
  54 for a relative pathname).
  55
  56 If the pathname given in
  57 .I pathname
  58 is relative and
  59 .I dirfd
  60 is the special value
  61 .BR AT_FDCWD ,
  62 then pathname is interpreted relative to the current working
  63 directory of the calling process (like
  64 .BR open (2)).
  65
  66 If the pathname given in
  67 .IR pathname
  68 is absolute, then
  69 .I dirfd
  70 is ignored.
  71 .SH "RETURN VALUE"
  72 .BR openat ()
  73 returns a new file descriptor, or \-1 if an error occurred
  74 (in which case,
  75 .I errno
  76 is set appropriately).
  77 .SH ERRORS
  78 The same errors that occur for
  79 .BR open (2)
  80 can also occur for
  81 .BR openat (2).
  82 The following additional errors can occur for
  83 .BR openat ():
  84 .TP
  85 .B EBADF
  86 .I dirfd
  87 is not a valid file descriptor.
  88 .TP
  89 .B ENOTDIR
  90 .I dirfd
  91 is a file descriptor referring to a file other than a directory.
  92 .SH NOTES
  93 The
  94 .BR openat ()
  95 system call (and similar system calls suffixed "at")
  96 provides functionality that can otherwise only be obtained
  97 less efficiently or at the risk of races in user applications.
  98 It allows the implementation of a per-thread "current working
  99 directory", via file descriptor(s) maintained by the application.
 100 (This functionality can also be obtained by tricks based
 101 on the use of
 102 .IR /proc/self/fd/ dirfd,
 103 but less efficiently.)
 104 It also allows the avoidance of various kinds of races that can occur
 105 as a result of directory deletions that may occur while an application
 106 is traversing a file system.
 107 .SH "CONFORMING TO"
 108 This system call is non-standard.
 109 A similar system call exists on Solaris.
 110 .\" The 'at' suffix in Solaris is actually double sensed.  It
 111 .\" primarily referred to "extended *at*tributes", which are
 112 .\" handled by Solaris' O_XATTR flag, but was also intended
 113 .\" to refer to the notion of "at a relative location".
 114 .\"
 115 .\" See also the following for a discussion of the inconsistent
 116 .\" naming of the *at() functions:
 117 .\" http://www.opengroup.org/austin/mailarchives/ag/msg09103.html
 118 .\" Subject:    RE: The naming of at()s is a difficult matter
 119 .\" From:       Don Cragun
 120 .\" Date:       Tue, 14 Feb 2006 14:56:50 -0800 (PST)
 121 .\"
 122 .SH VERSIONS
 123 .BR openat ()
 124 was added to Linux in kernel 2.6.16.
 125 .SH "SEE ALSO"
 126 .BR open (2),
 127 .BR path_resolution (2)