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     VOP_GETEXTATTR — retrieve named extended attribute from a vnode


     #include <sys/param.h>
     #include <sys/vnode.h>
     #include <sys/extattr.h>

     VOP_GETEXTATTR(struct vnode *vp, int attrnamespace, const char *name, struct uio *uio,
         size_t *size, struct ucred *cred, struct thread *td);


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

     Its arguments are:

     vp             The vnode of the file or directory.

     attrnamespace  Integer constant indicating which extended attribute namespace the attribute
                    name is present in.

     name           Pointer to a null-terminated character string containing the attribute name.

     uio            The location of the data to be read.

     size           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 NULL when size is not,
                    and vice versa.

     cred           The user credentials to use in authorizing the request.

     td             The thread requesting the extended attribute.

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


     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.


     [ENOATTR]          The requested attribute was not defined for this vnode.

     [EACCES]           The caller does not have the appropriate privilege.

     [ENXIO]            The request was not valid in this file system for the specified vnode and
                        attribute name.

     [ENOMEM]           Sufficient memory is not available to fulfill the request.

     [EFAULT]           The uio structure refers to an invalid userspace address.

     [EINVAL]           The name, namespace, or uio argument is invalid.

     [EOPNOTSUPP]       The file system does not support VOP_GETEXTATTR().


     extattr(9), vnode(9), VOP_LISTEXTATTR(9), VOP_SETEXTATTR(9)


     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.