175 lines
4.7 KiB
Groff
175 lines
4.7 KiB
Groff
.\"
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.\" Copyright (c) 2004 Apple Computer, Inc. All rights reserved.
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.\"
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.\" @APPLE_LICENSE_HEADER_START@
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.\"
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.\" This file contains Original Code and/or Modifications of Original Code
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.\" as defined in and that are subject to the Apple Public Source License
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.\" Version 2.0 (the 'License'). You may not use this file except in
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.\" compliance with the License. Please obtain a copy of the License at
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.\" http://www.opensource.apple.com/apsl/ and read it before using this
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.\" file.
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.\"
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.\" The Original Code and all software distributed under the License are
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.\" distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
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.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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.\" FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
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.\" Please see the License for the specific language governing rights and
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.\" limitations under the License.
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.\"
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.\" @APPLE_LICENSE_HEADER_END@
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.\"
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.Dd Oct 19, 2004
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.Dt GETXATTR 2
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.Os "Mac OS X"
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.Sh NAME
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.Nm getxattr,
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.Nm fgetxattr
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.Nd get an extended attribute value
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.Sh SYNOPSIS
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.Fd #include <sys/xattr.h>
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.Ft ssize_t
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.Fn getxattr "const char *path" "const char *name" "void *value" "size_t size" "u_int32_t position" "int options"
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.Ft ssize_t
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.Fn fgetxattr "int fd" "const char *name" "void *value" "size_t size" "u_int32_t position" "int options"
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.Sh DESCRIPTION
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Extended attributes extend the basic attributes of files and
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directories in the file system. They are stored as name:data pairs
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associated with file system objects (files, directories, symlinks, etc).
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.Pp
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The
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.Fn getxattr
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function retrieves up to
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.Fa size
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bytes of data from the extended attribute identified by
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.Fa name
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associated with
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.Fa path
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into the pre-allocated buffer pointed to by
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.Fa value .
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The function returns the number of bytes of data retrieved.
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.Pp
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An extended attribute's
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.Fa name
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is a simple NULL-terminated UTF-8 string.
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.Fa position
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specifies an offset within the extended attribute. In the current
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implementation, this argument is only used with the resource fork attribute.
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For all other extended attributes, this parameter is reserved and should
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be zero.
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.Pp
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On success,
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.Fa value
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contains the data associated with
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.Fa name .
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When
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.Fa value
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is set to NULL,
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.Fn getxattr
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returns current size of the named attribute. This facility can be used
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to determine the size of a buffer sufficiently large to hold the data
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currently associated with the attribute.
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.Pp
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.Fa options
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specify options for retrieving extended attributes:
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.Pp
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.Bl -tag -width XATTR_NOFOLLOW
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.It Dv XATTR_NOFOLLOW
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do not follow symbolic links.
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.Fn getxattr
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normally returns information from the target of
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.Fa path
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if it is a symbolic link. With this option,
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.Fn getxattr
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will return extended attribute data from the symbolic link instead.
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.It Dv XATTR_SHOWCOMPRESSION
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.Fn getxattr
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and
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.Fn fgetxattr
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will return HFS Plus Compression extended attribute
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.Fa name
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(if present) for the file referred to by
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.Fa path
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or
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.Fa fd .
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.El
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.Pp
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.Fn fgetxattr
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is identical to
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.Fn getxattr ,
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except that it retrieves extended attribute data from the open file
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referenced by the file descriptor
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.Fa fd .
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.Sh RETURN VALUES
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On success, the size of the extended attribute data is returned. On
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failure, -1 is returned and the global variable
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.Va errno
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is set as follows.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er ENOATTR
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The extended attribute does not exist.
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.It Bq Er ENOTSUP
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The file system does not support extended attributes or has the feature
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disabled.
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.It Bq Er ERANGE
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.Fa value
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(as indicated by
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.Fa size )
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is too small to hold the extended attribute data.
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.It Bq Er EPERM
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The named attribute is not permitted for this type of object.
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.It Bq Er EINVAL
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.Fa name
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is invalid or
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.Fa options
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has an unsupported bit set.
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.It Bq Er EISDIR
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.Fa path
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or
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.Fa fd
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do not refer to a regular file and the attribute in question is only
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applicable to files. Similar to EPERM.
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.It Bq Er ENOTDIR
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A component of
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.Fa path 's
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prefix is not a directory.
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.It Bq Er ENAMETOOLONG
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The length of
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.Fa name
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exceeds
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.Dv XATTR_MAXNAMELEN
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UTF-8 bytes, or a component of
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.Fa path
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exceeds
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.Dv NAME_MAX
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characters, or the entire
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.Fa path
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exceeds
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.Dv PATH_MAX
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characters.
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.It Bq Er EACCES
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Search permission is denied for a component of
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.Fa path
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or the attribute is not allowed to be read (e.g. an ACL prohibits reading
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the attributes of this file).
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er EFAULT
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.Fa path
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or
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.Fa name
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points to an invalid address.
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.It Bq Er EIO
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An I/O error occurred while reading from or writing to the file system.
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.El
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.Sh SEE ALSO
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.Xr listxattr 2 ,
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.Xr removexattr 2 ,
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.Xr setxattr 2
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.Sh HISTORY
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.Fn getxattr
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and
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.Fn fgetxattr
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first appeared in Mac OS X 10.4.
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