ATTR\_LIST(3) XFS Compatibility API ATTR\_LIST(3)

# [NAME](#NAME)

attr\_list, attr\_listf - list the names of the user attributes of a filesystem object

# [C SYNOPSIS](#C_SYNOPSIS)

```
#include <attr/attributes.h>

int attr_list (const char ∗path, char ∗buffer, 
               const int buffersize, int flags,
               attrlist_cursor_t ∗cursor);
```

```
int attr_listf (int fd, char ∗buffer, 
                const int buffersize, int flags,
                attrlist_cursor_t ∗cursor);
```

# [DESCRIPTION](#DESCRIPTION)

The **attr\_list** and **attr\_listf** functions provide a way to list the existing attributes of a filesystem object.

*Path* points to a path name for a filesystem object, and *fd* refers to the file descriptor associated with a file. The *buffer* will be filled with a structure describing at least a portion of the attributes associated with the given filesystem object. *Buffer* will be overwritten with an ***attrlist\_t*** structure containing a list of the attributes associated with that filesystem object, up to a maximum of *buffersize* bytes. The *buffer* must be sufficiently large to hold the appropriate data structures plus at least one maximally sized attribute name, but cannot be more than ATTR\_MAX\_VALUELEN (currently 64KB) bytes in length.

The contents of an ***attrlist\_t*** structure include the following members:

```
int32_t al_count; /∗ number of entries in attrlist ∗/
int32_t al_more; /∗ T/F: more attrs (do syscall again) ∗/
int32_t al_offset[1]; /∗ byte offsets of attrs [var-sized] ∗/
```

The *al\_count* field shows the number of attributes represented in this buffer, which is also the number of elements in the *al\_offset* array. The *al\_more* field will be non-zero if another **attr\_list** call would result in more attributes. The *al\_offset* array contains the byte offset within the *buffer* of the structure describing each of the attributes, an ***attrlist\_ent\_t*** structure. The ***ATTR\_ENTRY(buffer, index)*** macro will help with decoding the list. It takes a pointer to the *buffer* and an *index* into the *al\_offset* array and returns a pointer to the corresponding ***attrlist\_ent\_t*** structure.

The contents of an ***attrlist\_ent\_t*** structure include the following members:

```
uint32_t a_valuelen; /∗ number bytes in value of attr ∗/
char a_name[]; /∗ attr name (NULL terminated) ∗/
```

The *a\_valuelen* field shows the size in bytes of the value associated with the attribute whose name is stored in the *a\_name* field. The name is a NULL terminated string.

Note that the value of the attribute cannot be obtained through this interface, the **attr\_get** call should be used to get the value. The **attr\_list** interface tells the calling process how large of a buffer it must have in order to get the attribute's value.

The *flags* argument can contain the following symbols bitwise OR'ed together:

ATTR\_ROOT

List the attributes that are in the **root** address space, not in the **user** address space. (limited to use by super-user only)

ATTR\_DONTFOLLOW

Do not follow symbolic links when resolving a *path* on an **attr\_list** function call. The default is to follow symbolic links.

The *cursor* argument is a pointer to an opaque data structure that the kernel uses to track the calling process's position in the attribute list. The only valid operations on a *cursor* are to pass it into an **attr\_list** function call or to zero it out. It should be zero'ed out before the first **attr\_list** call. Note that multi-threaded applications may keep more than one *cursor* in order to serve multiple contexts, ie: the **attr\_list** call is "thread-safe".

**attr\_list** 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 was set in the *flag* argument that is not defined for this system call, or the buffer was too small or too large.

\[EFAULT]

Either *Path* or *buffer* points outside the allocated address space of the process, or *buffer* or *bufsize* are not 32bit aligned.

\[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*}.

\[ENOATTR]

*attribute* does not exist for this file.

**attr\_listf** will fail if:

\[EINVAL]

A bit was set in the *flag* argument that is not defined for this system call, or *fd* refers to a socket, not a file, or the buffer was too small or too large.

\[EFAULT]

Either *Path* or *buffer* points outside the allocated address space of the process, or *buffer* or *bufsize* are not 32bit aligned.

\[EBADF]

*Fd* does not refer to a valid descriptor.

# [DIAGNOSTICS](#DIAGNOSTICS)

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and *errno* is set to indicate the error.

# [SEE ALSO](#SEE_ALSO)

[**attr**(1)](/man/os/attr/attr.1), [**attr\_multi**(3)](/man/os/attr/attr_multi.3), [**attr\_remove**(3)](/man/os/attr/attr_remove.3), [**attr\_set**(3)](/man/os/attr/attr_set.3)

Extended Attributes Dec 2005

---

Document: attr_listf(3) from attr 2.6.0-r3 (Chainguard OS)
Source: https://git.savannah.nongnu.org/git/attr.git