man attr_multi – Man page for attr_multi

June 1, 2007 – 1:22 am

ATTR_MULTI

Section: XFS Compatibility API (3)
Updated: Extended Attributes
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NAME

attr_multi, attr_multif – manipulate multiple user attributes on a filesystem object at once
 

C SYNOPSIS

#include <attr/attributes.h>

int attr_multi (const char *path, attr_multiop_t *oplist, 

                int count, int flags);
int attr_multif (int fd, attr_multiop_t *oplist, 

                 int count, int flags);

[

 

DESCRIPTION

]

The
attr_multi

and
attr_multif

functions provide a way to operate on multiple attributes of a
filesystem object at once.

Path

points to a path name for a filesystem object, and
fd

refers to the file descriptor associated with a file.
The
oplist

is an array of attr_multiop_t structures.
Each element in that array describes a single attribute operation
and provides all the information required to carry out that operation
and to check for success or failure of that operation.
Count

tells how many elements are in the
oplist

array.

[c p a]

The contents of an attr_multiop_t structure include
the following members:

int am_opcode; /* which operation to perform (see below) */

int am_error; /* [out arg] result of this sub–op (an errno) */

char *am_attrname; /* attribute name to work with */

char *am_attrvalue; /* [in/out arg] attribute value (raw bytes) */

int am_length; /* [in/out arg] length of value */

int am_flags; /* flags (bit–wise OR of #defines below) */

The
am_opcode

field defines how the remaining fields are to be interpreted
and can take on one of the following values:

ATTR_OP_GET /* return the indicated attr’s value */

ATTR_OP_SET /* set/create the indicated attr/value pair */

ATTR_OP_REMOVE /* remove the indicated attr */

The
am_error

field will contain the appropriate error result code
if that sub–operation fails.
The result codes for a given sub–operation are a subset of
the result codes that are possible from the corresponding
single–attribute function call.
For example, the result code possible from an ATTR_OP_GET
sub–operation are a subset of those that can be returned from an
attr_get

function call.

The
am_attrname

field is a pointer to a NULL terminated string giving the attribute name
that the sub–operation should operate on.

The
am_attrvalue,

am_length

and
am_flags

fields are used to store the value of the named attribute,
and some control flags for that sub–operation, respectively.
Their use varies depending on the value of the
am_opcode

field.

ATTR_OP_GET

The
am_attrvalue

field is a pointer to a empty buffer that will be overwritten
with the value of the named attribute.
The
am_length

field is initially the total size of the memory buffer that the
am_attrvalue

field points to.
After the operation, the
am_length

field contains the actual size of the attribute’s value.
The
am_flags

field may be set to the ATTR_ROOT flag.
If the process has appropriate priviledges,
the ROOT namespace will be searched for the named attribute,
otherwise the USER namespace will be searched.

ATTR_OP_SET

The
am_attrvalue

and
am_length

fields contain the new value for the given attribute name and its length.
The ATTR_ROOT flag may be set in the
am_flags

field.
If the process has appropriate priviledges,
the ROOT namespace will be searched for the named attribute,
otherwise the USER namespace will be searched.
The ATTR_CREATE and the ATTR_REPLACE flags
may also be set in the
am_flags

field (but not simultaneously).
If the ATTR_CREATE flag is set,
the sub–operation will set the
am_error

field to EEXIST if the named attribute already exists.
If the ATTR_REPLACE flag is set,
the sub–operation will set the
am_error

field to ENOATTR if the named attribute does not already exist.
If neither of those two flags are set and the attribute does not exist,
then the attribute will be created with the given value.
If neither of those two flags are set and the attribute already exists,
then the value will be replaced with the given value.

ATTR_OP_REMOVE

The
am_attrvalue

and
am_length

fields are not used and are ignored.
The
am_flags

field may be set to the ATTR_ROOT flag.
If the process has appropriate priviledges,
the ROOT namespace will be searched for the named attribute,
otherwise the USER namespace will be searched.

The
flags

argument to the
attr_multi

call is used to control following of symbolic links in the
path

argument.
The default is to follow symbolic links,
flags

should be set to ATTR_DONTFOLLOW to not follow symbolic links.

attr_multi

will fail if one or more of the following are true:

[ENOENT]

The named file does not exist.

[EPERM]

The effective user
ID
does not match the owner of the file
and the effective user
ID
is not super–user.

[ENOTDIR]

A component of the
path prefix
is not a directory.

[EACCES]

Search permission is denied on a
component of the
path prefix.

[EINVAL]

A bit other than ATTR_DONTFOLLOW was set in the
flag

argument.

[EFAULT]

Path,

or
oplist

points outside the allocated address space of the process.

[ELOOP]

A path name lookup involved too many symbolic links.

[ENAMETOOLONG]

The length of
path

exceeds
{MAXPATHLEN},

or a pathname component is longer than
{MAXNAMELEN}.

attr_multif

will fail if:

[EINVAL]

A bit was set in the
flag

argument, or
fd

refers to a socket, not a file.

[EFAULT]

Oplist

points outside the allocated address space of the process.

[EBADF]

Fd

does not refer to a valid descriptor.

 

DIAGNOSTICS

On success, zero is returned. On error, –1 is returned, and
errno

is set appropriately.
Note that the individual operations listed in the
oplist

array each have their own error return fields.
The
errno

variable only records the result of the
attr_multi

call itself, not the result of any of the sub–operations.
 

SEE ALSO

attr(1),

attr_get(3),

attr_list(3),

attr_remove(3),

and
attr_set(3).

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Index

NAME

C SYNOPSIS

DESCRIPTION

DIAGNOSTICS

SEE ALSO

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Related posts:

1. man attr_multif – Man page for attr_multif
2. man attr_remove – Man page for attr_remove
3. man attr_get – Man page for attr_get
4. man attr_list – Man page for attr_list
5. man lsetxattr – Man page for lsetxattr
6. man IPC::Semaphore – Man page for IPC::Semaphore
7. man field_pad – Man page for field_pad
8. man field_fore – Man page for field_fore
9. man lgetxattr – Man page for lgetxattr
10. man removexattr – Man page for removexattr