man2/getxattr.2

   1 .\" Extended attributes system calls manual pages
   2 .\"
   3 .\" Copyright (C) Andreas Gruenbacher, February 2001
   4 .\" Copyright (C) Silicon Graphics Inc, September 2001
   5 .\"
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  27 .TH GETXATTR 2 2013-01-19 "Linux" "Linux Programmer's Manual"
  28 .SH NAME
  29 getxattr, lgetxattr, fgetxattr \- retrieve an extended attribute value
  30 .SH SYNOPSIS
  31 .fam C
  32 .nf
  33 .B #include <sys/types.h>
  34 .B #include <attr/xattr.h>
  35 .sp
  36 .BI "ssize_t getxattr(const char\ *" path ", const char\ *" name ,
  37 .BI "                 void\ *" value ", size_t " size );
  38 .BI "ssize_t lgetxattr(const char\ *" path ", const char\ *" name ,
  39 .BI "                 void\ *" value ", size_t " size );
  40 .BI "ssize_t fgetxattr(int " fd ", const char\ *" name ,
  41 .BI "                 void\ *" value ", size_t " size );
  42 .fi
  43 .fam T
  44 .SH DESCRIPTION
  45 Extended attributes are
  46 .IR name :\c
  47 .I value
  48 pairs associated with inodes (files, directories, symbolic links, etc.).
  49 They are extensions to the normal attributes which are associated
  50 with all inodes in the system (i.e., the
  51 .BR stat (2)
  52 data).
  53 A complete overview of extended attributes concepts can be found in
  54 .BR attr (5).
  55 .PP
  56 .BR getxattr ()
  57 retrieves the
  58 .I value
  59 of the extended attribute identified by
  60 .I name
  61 and associated with the given
  62 .I path
  63 in the file system.
  64 The length of the attribute
  65 .I value
  66 is returned.
  67 .PP
  68 .BR lgetxattr ()
  69 is identical to
  70 .BR getxattr (),
  71 except in the case of a symbolic link, where the link itself is
  72 interrogated, not the file that it refers to.
  73 .PP
  74 .BR fgetxattr ()
  75 is identical to
  76 .BR getxattr (),
  77 only the open file referred to by
  78 .I fd
  79 (as returned by
  80 .BR open (2))
  81 is interrogated in place of
  82 .IR path .
  83 .PP
  84 An extended attribute
  85 .I name
  86 is a simple null-terminated string.
  87 The name includes a namespace prefix; there may be several, disjoint
  88 namespaces associated with an individual inode.
  89 The value of an extended attribute is a chunk of arbitrary textual or
  90 binary data of specified length.
  91 .PP
  92 An empty buffer of
  93 .I size
  94 zero can be passed into these calls to return the current size of the
  95 named extended attribute, which can be used to estimate the size of a
  96 buffer which is sufficiently large to hold the value associated with
  97 the extended attribute.
  98 .PP
  99 The interface is designed to allow guessing of initial buffer
 100 sizes, and to enlarge buffers when the return value indicates
 101 that the buffer provided was too small.
 102 .SH RETURN VALUE
 103 On success, a positive number is returned indicating the size of the
 104 extended attribute value.
 105 On failure, \-1 is returned and
 106 .I errno
 107 is set appropriately.
 108 .SH ERRORS
 109 .TP
 110 .B ENOATTR
 111 The named attribute does not exist, or the process has no access to
 112 this attribute.
 113 .RB ( ENOATTR
 114 is defined to be a synonym for
 115 .BR ENODATA
 116 in
 117 .IR <attr/xattr.h> .)
 118 .TP
 119 .B ENOTSUP
 120 Extended attributes are not supported by the file system, or are disabled.
 121 .TP
 122 .B ERANGE
 123 The
 124 .I size
 125 of the
 126 .I value
 127 buffer is too small to hold the result.
 128 .PP
 129 In addition, the errors documented in
 130 .BR stat (2)
 131 can also occur.
 132 .SH VERSIONS
 133 These system calls have been available on Linux since kernel 2.4;
 134 glibc support is provided since version 2.3.
 135 .SH CONFORMING TO
 136 These system calls are Linux-specific.
 137 .\" .SH AUTHORS
 138 .\" Andreas Gruenbacher,
 139 .\" .RI < a.gruenbacher@computer.org >
 140 .\" and the SGI XFS development team,
 141 .\" .RI < linux-xfs@oss.sgi.com >.
 142 .\" Please send any bug reports or comments to these addresses.
 143 .SH SEE ALSO
 144 .BR getfattr (1),
 145 .BR setfattr (1),
 146 .BR listxattr (2),
 147 .BR open (2),
 148 .BR removexattr (2),
 149 .BR setxattr (2),
 150 .BR stat (2),
 151 .BR attr (5),
 152 .BR symlink (7)