man2/getxattr.2

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   2 .\" Extended attributes system calls manual pages
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   4 .\" (C) Andreas Gruenbacher, February 2001
   5 .\" (C) Silicon Graphics Inc, September 2001
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  27 .TH GETXATTR 2 "Extended Attributes" "Dec 2001" "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 "\t\t\t\t void\ *" value ", size_t " size );
  38 .BI "ssize_t lgetxattr (const char\ *" path ", const char\ *" name ",
  39 .BI "\t\t\t\t void\ *" value ", size_t " size );
  40 .BI "ssize_t fgetxattr (int " filedes ", const char\ *" name ",
  41 .BI "\t\t\t\t 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, symlinks, 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 filesystem.
  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 pointed to by
  78 .I filedes
  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 .PP
 109 If the named attribute does not exist, or the process has no access to
 110 this attribute,
 111 .I errno
 112 is set to ENOATTR.
 113 .PP
 114 If the
 115 .I size
 116 of the
 117 .I value
 118 buffer is too small to hold the result,
 119 .I errno
 120 is set to ERANGE.
 121 .PP
 122 If extended attributes are not supported by the filesystem, or are disabled,
 123 .I errno
 124 is set to ENOTSUP.
 125 .PP
 126 The errors documented for the
 127 .BR stat (2)
 128 system call are also applicable here.
 129 .SH AUTHORS
 130 Andreas Gruenbacher,
 131 .RI < a.gruenbacher@computer.org >
 132 and the SGI XFS development team,
 133 .RI < linux-xfs@oss.sgi.com >.
 134 Please send any bug reports or comments to these addresses.
 135 .SH SEE ALSO
 136 .BR getfattr (1),
 137 .BR setfattr (1),
 138 .BR listxattr (2),
 139 .BR open (2),
 140 .BR removexattr (2),
 141 .BR setxattr (2),
 142 .BR stat (2),
 143 .BR attr (5)