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e324bf91e8
extattr_set_{fd,file,link} is logically a write(2)-like operation and
should return ssize_t, just like extattr_get_*. Also, the user-space
utility was using an int for the return value of extattr_get_* and
extattr_list_*, both of which return an ssize_t.
MFC after: 1 week
277 lines
8.1 KiB
Groff
277 lines
8.1 KiB
Groff
.\"
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.\" Copyright (c) 2001 Dima Dorfman <dima@unixfreak.org>
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.\" Copyright (c) 2003 Robert Watson <rwatson@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 29, 2008
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.Dt EXTATTR 2
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.Os
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.Sh NAME
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.Nm extattr_get_fd ,
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.Nm extattr_set_fd ,
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.Nm extattr_delete_fd ,
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.Nm extattr_list_fd ,
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.Nm extattr_get_file ,
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.Nm extattr_set_file ,
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.Nm extattr_delete_file ,
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.Nm extattr_list_file ,
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.Nm extattr_get_link ,
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.Nm extattr_set_link ,
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.Nm extattr_delete_link ,
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.Nm extattr_list_link
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.Nd system calls to manipulate VFS extended attributes
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/extattr.h
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.Ft ssize_t
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.Fn extattr_get_fd "int fd" "int attrnamespace" "const char *attrname" "void *data" "size_t nbytes"
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.Ft ssize_t
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.Fn extattr_set_fd "int fd" "int attrnamespace" "const char *attrname" "const void *data" "size_t nbytes"
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.Ft int
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.Fn extattr_delete_fd "int fd" "int attrnamespace" "const char *attrname"
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.Ft ssize_t
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.Fn extattr_list_fd "int fd" "int attrnamespace" "void *data" "size_t nbytes"
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.Ft ssize_t
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.Fn extattr_get_file "const char *path" "int attrnamespace" "const char *attrname" "void *data" "size_t nbytes"
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.Ft ssize_t
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.Fn extattr_set_file "const char *path" "int attrnamespace" "const char *attrname" "const void *data" "size_t nbytes"
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.Ft int
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.Fn extattr_delete_file "const char *path" "int attrnamespace" "const char *attrname"
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.Ft ssize_t
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.Fn extattr_list_file "const char *path" "int attrnamespace" "void *data" "size_t nbytes"
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.Ft ssize_t
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.Fn extattr_get_link "const char *path" "int attrnamespace" "const char *attrname" "void *data" "size_t nbytes"
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.Ft ssize_t
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.Fn extattr_set_link "const char *path" "int attrnamespace" "const char *attrname" "const void *data" "size_t nbytes"
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.Ft int
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.Fn extattr_delete_link "const char *path" "int attrnamespace" "const char *attrname"
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.Ft ssize_t
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.Fn extattr_list_link "const char *path" "int attrnamespace" "void *data" "size_t nbytes"
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.Sh DESCRIPTION
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Named extended attributes are meta-data associated with vnodes
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representing files and directories.
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They exist as
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.Qq Li name=value
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pairs within a set of namespaces.
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.Pp
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The
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.Fn extattr_get_file
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system call retrieves the value of the specified extended attribute into
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a buffer pointed to by
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.Fa data
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of size
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.Fa nbytes .
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The
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.Fn extattr_set_file
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system call sets the value of the specified extended attribute to the data
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described by
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.Fa data .
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The
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.Fn extattr_delete_file
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system call deletes the extended attribute specified.
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The
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.Fn extattr_list_file
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returns a list of attributes present in the requested namespace.
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Each list entry consists of a single byte containing the length
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of the attribute name, followed by the attribute name.
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The attribute name is not terminated by ASCII 0 (nul).
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The
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.Fn extattr_get_file ,
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and
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.Fn extattr_list_file
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calls consume the
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.Fa data
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and
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.Fa nbytes
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arguments in the style of
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.Xr read 2 ;
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.Fn extattr_set_file
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consumes these arguments in the style of
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.Xr write 2 .
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.Pp
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If
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.Fa data
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is
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.Dv NULL
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in a call to
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.Fn extattr_get_file
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and
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.Fn extattr_list_file
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then the size of defined extended attribute data will be returned, rather
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than the quantity read, permitting applications to test the size of the
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data without performing a read.
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The
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.Fn extattr_delete_link ,
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.Fn extattr_get_link ,
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and
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.Fn extattr_set_link
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system calls behave in the same way as their _file counterparts, except that
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they do not follow symlinks.
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.Pp
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The
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.Fn extattr_get_fd ,
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.Fn extattr_set_fd ,
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.Fn extattr_delete_fd ,
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and
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.Fn extattr_list_fd ,
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calls are identical to their
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.Qq Li _file
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counterparts except for the first argument.
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The
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.Qq Li _fd
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functions take a file descriptor, while the
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.Qq Li _file
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functions take a path.
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Both arguments describe a file associated with the extended attribute
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that should be manipulated.
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.Pp
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The following arguments are common to all the system calls described here:
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.Bl -tag -width attrnamespace
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.It Fa attrnamespace
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the namespace in which the extended attribute resides; see
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.Xr extattr 9
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.It Fa attrname
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the name of the extended attribute
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.El
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.Pp
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Named extended attribute semantics vary by file system implementing the call.
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Not all operations may be supported for a particular attribute.
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Additionally, the format of the data in
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.Fa data
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is attribute-specific.
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.Pp
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For more information on named extended attributes, please see
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.Xr extattr 9 .
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.Sh CAVEAT
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This interface is under active development, and as such is subject to
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change as applications are adapted to use it.
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Developers are discouraged from relying on its stability.
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.Sh RETURN VALUES
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If successful, the
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.Fn extattr_get_file ,
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.Fn extattr_set_file ,
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and
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.Fn extattr_list_file
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calls return the number of bytes
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that were read or written from the
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.Fa data ,
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respectively, or if
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.Fa data
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was
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.Dv NULL ,
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then
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.Fn extattr_get_file
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and
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.Fn extattr_list_file
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return the number of bytes available to read.
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If any of the calls are unsuccessful, the value \-1 is returned
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and the global variable
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.Va errno
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is set to indicate the error.
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.Pp
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.Rv -std extattr_delete_file
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.Sh ERRORS
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The following errors may be returned by the system calls themselves.
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Additionally, the file system implementing the call may return any
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other errors it desires.
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.Bl -tag -width Er
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.It Bq Er EFAULT
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The
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.Fa attrnamespace
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and
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.Fa attrname
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arguments,
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or the memory range defined by
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.Fa data
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and
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.Fa nbytes
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point outside the process's allocated address space.
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.It Bq Er ENAMETOOLONG
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The attribute name was longer than
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.Dv EXTATTR_MAXNAMELEN .
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.El
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.Pp
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The
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.Fn extattr_get_fd ,
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.Fn extattr_set_fd ,
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.Fn extattr_delete_fd ,
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and
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.Fn extattr_list_fd
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system calls may also fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The file descriptor referenced by
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.Fa fd
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was invalid.
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.El
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.Pp
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Additionally, the
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.Fn extattr_get_file ,
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.Fn extattr_set_file ,
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and
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.Fn extattr_delete_file
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calls may also fail due to the following errors:
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.Bl -tag -width Er
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.It Bq Er ENOATTR
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The requested attribute was not defined for this file.
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.It Bq Er ENOTDIR
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A component of the path prefix is not a directory.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded 255 characters,
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or an entire path name exceeded 1023 characters.
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.It Bq Er ENOENT
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A component of the path name that must exist does not exist.
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.It Bq Er EACCES
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Search permission is denied for a component of the path prefix.
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.\" XXX are any missing?
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.El
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.Sh SEE ALSO
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.Xr extattr 3 ,
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.Xr getextattr 8 ,
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.Xr setextattr 8 ,
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.Xr extattr 9 ,
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.Xr VOP_GETEXTATTR 9 ,
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.Xr VOP_SETEXTATTR 9
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.Sh HISTORY
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Extended attribute support was developed as part of the
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.Tn TrustedBSD
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Project, and introduced in
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.Fx 5.0 .
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It was developed to support security extensions requiring additional labels
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to be associated with each file or directory.
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.Sh BUGS
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In earlier versions of this API, passing an empty string for the
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attribute name to
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.Fn extattr_get_fd ,
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.Fn extattr_get_file ,
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or
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.Fn extattr_get_link
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would return the list of attributes defined for the target object.
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This interface has been deprecated in preference to using the explicit
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list API, and should not be used.
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