man2/getxattr.2

   1 .\" Copyright (C) Andreas Gruenbacher, February 2001
   2 .\" Copyright (C) Silicon Graphics Inc, September 2001
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  25 .TH GETXATTR 2 2019-03-06 "Linux" "Linux Programmer's Manual"
  26 .SH NAME
  27 getxattr, lgetxattr, fgetxattr \- retrieve an extended attribute value
  28 .SH SYNOPSIS
  29 .fam C
  30 .nf
  31 .B #include <sys/types.h>
  32 .B #include <sys/xattr.h>
  33 .PP
  34 .BI "ssize_t getxattr(const char\ *" path ", const char\ *" name ,
  35 .BI "                 void\ *" value ", size_t " size );
  36 .BI "ssize_t lgetxattr(const char\ *" path ", const char\ *" name ,
  37 .BI "                 void\ *" value ", size_t " size );
  38 .BI "ssize_t fgetxattr(int " fd ", const char\ *" name ,
  39 .BI "                 void\ *" value ", size_t " size );
  40 .fi
  41 .fam T
  42 .SH DESCRIPTION
  43 Extended attributes are
  44 .IR name :\c
  45 .I value
  46 pairs associated with inodes (files, directories, symbolic links, etc.).
  47 They are extensions to the normal attributes which are associated
  48 with all inodes in the system (i.e., the
  49 .BR stat (2)
  50 data).
  51 A complete overview of extended attributes concepts can be found in
  52 .BR xattr (7).
  53 .PP
  54 .BR getxattr ()
  55 retrieves the value of the extended attribute identified by
  56 .I name
  57 and associated with the given
  58 .I path
  59 in the filesystem.
  60 The attribute value is placed in the buffer pointed to by
  61 .IR value ;
  62 .I size
  63 specifies the size of that buffer.
  64 The return value of the call is the number of bytes placed in
  65 .IR value .
  66 .PP
  67 .BR lgetxattr ()
  68 is identical to
  69 .BR getxattr (),
  70 except in the case of a symbolic link, where the link itself is
  71 interrogated, not the file that it refers to.
  72 .PP
  73 .BR fgetxattr ()
  74 is identical to
  75 .BR getxattr (),
  76 only the open file referred to by
  77 .I fd
  78 (as returned by
  79 .BR open (2))
  80 is interrogated in place of
  81 .IR path .
  82 .PP
  83 An extended attribute
  84 .I name
  85 is a null-terminated string.
  86 The name includes a namespace prefix; there may be several, disjoint
  87 namespaces associated with an individual inode.
  88 The value of an extended attribute is a chunk of arbitrary textual or
  89 binary data that was assigned using
  90 .BR setxattr (2).
  91 .PP
  92 If
  93 .I size
  94 is specified as zero, these calls return the current size of the
  95 named extended attribute (and leave
  96 .I value
  97 unchanged).
  98 This can be used to determine the size of the buffer that
  99 should be supplied in a subsequent call.
 100 (But, bear in mind that there is a possibility that the
 101 attribute value may change between the two calls,
 102 so that it is still necessary to check the return status
 103 from the second call.)
 104 .SH RETURN VALUE
 105 On success, these calls return a nonnegative value which is
 106 the size (in bytes) of the extended attribute value.
 107 On failure, \-1 is returned and
 108 .I errno
 109 is set appropriately.
 110 .SH ERRORS
 111 .TP
 112 .B E2BIG
 113 The size of the attribute value is larger than the maximum size allowed; the
 114 attribute cannot be retrieved.
 115 This can happen on filesystems that support
 116 very large attribute values such as NFSv4, for example.
 117 .TP
 118 .B ENODATA
 119 The named attribute does not exist, or the process has no access to
 120 this attribute.
 121 .\" .RB ( ENOATTR
 122 .\" is defined to be a synonym for
 123 .\" .BR ENODATA
 124 .\" in
 125 .\" .IR <attr/attributes.h> .)
 126 .TP
 127 .B ENOTSUP
 128 Extended attributes are not supported by the filesystem, or are disabled.
 129 .TP
 130 .B ERANGE
 131 The
 132 .I size
 133 of the
 134 .I value
 135 buffer is too small to hold the result.
 136 .PP
 137 In addition, the errors documented in
 138 .BR stat (2)
 139 can also occur.
 140 .SH VERSIONS
 141 These system calls have been available on Linux since kernel 2.4;
 142 glibc support is provided since version 2.3.
 143 .SH CONFORMING TO
 144 These system calls are Linux-specific.
 145 .\" .SH AUTHORS
 146 .\" Andreas Gruenbacher,
 147 .\" .RI < a.gruenbacher@computer.org >
 148 .\" and the SGI XFS development team,
 149 .\" .RI < linux-xfs@oss.sgi.com >.
 150 .\" Please send any bug reports or comments to these addresses.
 151 .SH EXAMPLE
 152 See
 153 .BR listxattr (2).
 154 .SH SEE ALSO
 155 .BR getfattr (1),
 156 .BR setfattr (1),
 157 .BR listxattr (2),
 158 .BR open (2),
 159 .BR removexattr (2),
 160 .BR setxattr (2),
 161 .BR stat (2),
 162 .BR symlink (7),
 163 .BR xattr (7)