man VOP_GETEXTATTR (9): retrieve named extended attribute from a vnode

SYNOPSIS

In sys/param.h In sys/vnode.h In sys/extattr.h Ft int Fo VOP_GETEXTATTR Fa struct vnode *vp Fa int attrnamespace Fa const char *name Fa struct uio *uio Fa size_t *size Fa struct ucred *cred Fa struct thread *td Fc

DESCRIPTION

This vnode call may be used to retrieve a specific named extended attribute from a file or directory.

Its arguments are:

Fa vp: The vnode of the file or directory.
Fa attrnamespace: Integer constant indicating which extended attribute namespace the attribute name is present in.
Fa name: Pointer to a null-terminated character string containing the attribute name.
Fa uio: The location of the data to be read.
Fa size: If not NULL on return it will contain the number of bytes required to read all of the attribute data. In most cases Fa uio will be NULL when Fa size is not, and vice versa.
Fa cred: The user credentials to use in authorizing the request.
Fa td: The thread requesting the extended attribute.

The Fa cred pointer may be NULL to indicate that access control checks are not to be performed, if possible. This Fa cred 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 extattr(9).

LOCKS

The vnode will be locked on entry and should remain locked on return.

RETURN VALUES

On success, zero will be returned, and the uio structure will be updated to reflect data read. Otherwise, an appropriate error code is returned.

ERRORS

Bq Er ENOATTR: The requested attribute was not defined for this vnode.
Bq Er EACCES: The caller does not have the appropriate privilege.
Bq Er ENXIO: The request was not valid in this file system for the specified vnode and attribute name.
Bq Er ENOMEM: Sufficient memory is not available to fulfill the request.
Bq Er EFAULT: The uio structure refers to an invalid userspace address.
Bq Er EINVAL: The Fa name , Fa namespace , or Fa uio argument is invalid.
Bq Er EOPNOTSUPP: The file system does not support Fn VOP_GETEXTATTR .

BUGS

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.