retrieve named extended attribute from a vnode
, int attrnamespace
const char *name
struct uio *uio
struct ucred *cred
struct thread *td
This vnode call may be used to retrieve a specific named extended attribute from
a file or directory.
Its arguments are:
- The vnode of the file or directory.
- Integer constant indicating which extended attribute namespace the
attribute name is present in.
- Pointer to a null-terminated character string containing the attribute
- The location of the data to be read.
- If not
NULL, on return it will contain
the number of bytes required to read all of the attribute data. In most
cases uio will be
size is not, and vice versa.
- The user credentials to use in authorizing the request.
- The thread requesting the extended attribute.
pointer may be
to indicate that access control checks
are not to be performed, if possible. This
setting might be used to allow the
kernel to authorize extended attribute retrieval that the active process might
not be permitted to do.
Extended attribute semantics may vary by file system implementing the call. More
information on extended attributes may be found in
The vnode will be locked on entry and should remain locked on return.
On success, zero will be returned, and the uio structure will be updated to
reflect data read. Otherwise, an appropriate error code is returned.
- The requested attribute was not defined for this vnode.
- The caller does not have the appropriate privilege.
- The request was not valid in this file system for the specified vnode and
- Sufficient memory is not available to fulfill the request.
- The uio structure refers to an invalid userspace address.
- The name,
uio argument is invalid.
- The file system does not support
By passing in the empty string as the attribute name, some file systems will
return a list of defined names on the target vnode for the requested
namespace. This is a bad API, and will be replaced by an explicit VOP.