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attribute. Also define some macros to manipulate one of these
structures. Explain their use in the extattr.9 manual page.
The next step will be to make a sweep through the kernel replacing
the old pointer manipulation code. To get an idea of how they would
be used, the ffs_findextattr() function in ufs/ffs/ffs_vnops.c is
currently written as follows:
/*
* Vnode operating to retrieve a named extended attribute.
*
* Locate a particular EA (nspace:name) in the area (ptr:length), and return
* the length of the EA, and possibly the pointer to the entry and to the data.
*/
static int
ffs_findextattr(u_char *ptr, u_int length, int nspace, const char *name,
u_char **eap, u_char **eac)
{
u_char *p, *pe, *pn, *p0;
int eapad1, eapad2, ealength, ealen, nlen;
uint32_t ul;
pe = ptr + length;
nlen = strlen(name);
for (p = ptr; p < pe; p = pn) {
p0 = p;
bcopy(p, &ul, sizeof(ul));
pn = p + ul;
/* make sure this entry is complete */
if (pn > pe)
break;
p += sizeof(uint32_t);
if (*p != nspace)
continue;
p++;
eapad2 = *p++;
if (*p != nlen)
continue;
p++;
if (bcmp(p, name, nlen))
continue;
ealength = sizeof(uint32_t) + 3 + nlen;
eapad1 = 8 - (ealength % 8);
if (eapad1 == 8)
eapad1 = 0;
ealength += eapad1;
ealen = ul - ealength - eapad2;
p += nlen + eapad1;
if (eap != NULL)
*eap = p0;
if (eac != NULL)
*eac = p;
return (ealen);
}
return(-1);
}
After applying the structure and macros, it would look like this:
/*
* Vnode operating to retrieve a named extended attribute.
*
* Locate a particular EA (nspace:name) in the area (ptr:length), and return
* the length of the EA, and possibly the pointer to the entry and to the data.
*/
static int
ffs_findextattr(u_char *ptr, u_int length, int nspace, const char *name,
u_char **eapp, u_char **eac)
{
struct extattr *eap, *eaend;
eaend = (struct extattr *)(ptr + length);
for (eap = (struct extattr *)ptr; eap < eaend; eap = EXTATTR_NEXT(eap)){
/* make sure this entry is complete */
if (EXTATTR_NEXT(eap) > eaend)
break;
if (eap->ea_namespace != nspace ||
eap->ea_namelength != length ||
bcmp(eap->ea_name, name, length))
continue;
if (eapp != NULL)
*eapp = eap;
if (eac != NULL)
*eac = EXTATTR_CONTENT(eap);
return (EXTATTR_CONTENT_SIZE(eap));
}
return(-1);
}
Not only is it considerably shorter, but it hopefully more readable :-)
152 lines
5.8 KiB
Groff
152 lines
5.8 KiB
Groff
.\"-
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.\" Copyright (c) 1999, 2000, 2001, 2003 Robert N. M. Watson
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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 December 23, 1999
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.Os
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.Dt EXTATTR 9
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.Sh NAME
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.Nm extattr
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.Nd virtual file system named extended attributes
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/vnode.h
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.In sys/extattr.h
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.Sh DESCRIPTION
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Named extended attributes allow additional meta-data to be associated
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with vnodes representing files and directories.
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The semantics of this additional data is that of a "name=value" pair, where
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a name may be defined or undefined, and if defined, associated with zero or
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more bytes of arbitrary binary data.
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Extended attribute names exist within a set of namespaces; each operation
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on an extended attribute is required to provide the namespace to which to
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operation refers.
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If the same name is present in multiple namespaces, the extended attributes
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associated with the names are stored and manipulated independently.
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The following two namespaces are defined universally, although individual
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file systems may implement additional namespaces, or not implement
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these namespaces:
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.Dv EXTATTR_NAMESPACE_USER ,
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.Dv EXTATTR_NAMESPACE_SYSTEM .
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The semantics of these attributes are intended to be as follows: user
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attribute data is protected according the normal discretionary
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and mandatory protections associated with the data in the file or
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directory; system attribute data is protected such that appropriate
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privilege is required to directly access or manipulate these attributes.
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.Pp
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Reads of extended attribute data may return specific contiguous regions of
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the meta-data, in the style of
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.Xr VOP_READ 9 ,
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but writes will replace the entire current "value" associated with
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a given name.
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As there are a plethora of file systems with differing extended attributes,
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availability and functionality of these functions may be limited, and they
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should be used with awareness of the underlying semantics of the supporting
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file system.
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Authorization schemes for extended attribute data may also vary by file
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system, as well as maximum attribute size, and whether or not any or
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specific new attributes may be defined.
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.Pp
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Extended attributes are named using a null-terminated character string.
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Depending on underlying file system semantics, this name may or may not be
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case-sensitive.
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Appropriate vnode extended attribute calls are:
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.Xr VOP_GETEXTATTR 9 ,
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.Xr VOP_LISTEXTATTR 9 ,
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and
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.Xr VOP_SETEXTATTR 9 .
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.Pp
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The format of an external attribute is defined by the extattr structure:
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.Bd -literal
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struct extattr {
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int32_t ea_length; /* length of this attribute */
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int8_t ea_namespace; /* name space of this attribute */
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int8_t ea_contentpadlen; /* padding at end of attribute */
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int8_t ea_namelength; /* length of attribute name */
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char ea_name[1]; /* null-terminated attribute name */
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/* extended attribute content follows */
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};
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.Ed
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.Pp
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Several macros are defined to manipulate these structures.
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Each macro takes a pointer to an extattr structure.
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.Bl -tag -width ".Dv EXTATTR_SET_LENGTHS(eap, size)"
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.It Dv EXTATTR_NEXT(eap)
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Returns a pointer to the next extended attribute following
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.Fa eap .
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.It Dv EXTATTR_CONTENT(eap)
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Returns a pointer to the extended attribute content referenced by
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.Fa eap .
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.It Dv EXTATTR_CONTENT_SIZE(eap)
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Returns the size of the extended attribute content referenced by
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.Fa eap .
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.It Dv EXTATTR_SET_LENGTHS(eap, size)
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Called with the size of the attribute content after initializing
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the attribute name to calculate and set the
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.Fa ea_length ,
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.Fa ea_namelength ,
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and
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.Fa ea_contentpadlen
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fields of the extended attribute structure.
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.El
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.Pp
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The following code identifies an ACL:
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.Bd -literal
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if (eap->ea_namespace == EXTATTR_NAMESPACE_SYSTEM &&
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!strcmp(eap->ea_name, POSIX1E_ACL_ACCESS_EXTATTR_NAME) {
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aclp = EXTATTR_CONTENT(eap);
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acllen = EXTATTR_CONTENT_SIZE(eap);
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...
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}
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.Ed
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.Pp
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The following code creates an extended attribute
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containing a copy of a structure
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.Fa mygif :
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.Bd -literal
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eap->ea_namespace = EXTATTR_NAMESPACE_USER;
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strcpy(eap->ea_name, "filepic.gif");
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EXTATTR_SET_LENGTHS(eap, sizeof(struct mygif));
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memcpy(EXTATTR_CONTENT(eap), &mygif, sizeof(struct mygif));
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.Ed
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.Pp
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.Sh SEE ALSO
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.Xr VFS 9 ,
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.Xr VFS_EXTATTRCTL 9 ,
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.Xr VOP_GETEXTATTR 9 ,
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.Xr VOP_LISTEXTATTR 9 ,
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.Xr VOP_SETEXTATTR 9
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.Sh AUTHORS
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This manual page was written by
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.An Robert Watson .
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.Sh BUGS
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In addition, the interface does not provide a mechanism to retrieve
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the current set of available attributes; it has been suggested that
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providing a
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.Dv NULL
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attribute name should cause a list of defined attributes for the passed file
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or directory, but this is not currently implemented.
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