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CentOS 7.0 - man page for attr_list (centos section 3)

ATTR_LIST(3)					XFS Compatibility API					 ATTR_LIST(3)

NAME
attr_list, attr_listf - list the names of the user attributes of a filesystem object
C SYNOPSIS
#include <sys/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
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 ele- ments 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: u_int32_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
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
attr(1), attr_multi(3), attr_remove(3), and attr_set(3). Dec 2005 Extended Attributes ATTR_LIST(3)


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