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VOP_ACCESS(9)		 BSD Kernel Developer's	Manual		 VOP_ACCESS(9)

NAME
     VOP_ACCESS	-- check access	permissions of a file or Unix domain socket

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

     int
     VOP_ACCESS(struct vnode *vp, int mode, struct ucred *cred,
	 struct	thread *td);

DESCRIPTION
     This entry	point checks the access	permissions of the file	against	the
     given credentials.

     Its arguments are:

     vp	   the vnode of	the file to check

     mode  the type of access required

     cred  the user credentials	to check

     td	   the thread which is checking

     The mode is a mask	which can contain VREAD, VWRITE	or VEXEC.

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

RETURN VALUES
     If	the file is accessible in the specified	way, then zero is returned,
     otherwise an appropriate error code is returned.

PSEUDOCODE
     int
     vop_access(struct vnode *vp, int mode, struct ucred *cred,	struct thread *td)
     {
	 int error;

	 /*
	  * Disallow write attempts on read-only file systems;
	  * unless the file is a socket, fifo, or a block or
	  * character device resident on the filesystem.
	  */
	 if (mode & VWRITE) {
	     switch (vp->v_type) {
	     case VDIR:
	     case VLNK:
	     case VREG:
		 if (vp->v_mount->mnt_flag & MNT_RDONLY)
		     return EROFS;

		 break;
	     }
	 }

	 /* If immutable bit set, nobody gets to write it. */
	 if ((mode & VWRITE) &&	vp has immutable bit set)
	     return EPERM;

	 /* Otherwise, user id 0 always	gets access. */
	 if (cred->cr_uid == 0)
	     return 0;

	 mask =	0;

	 /* Otherwise, check the owner.	*/
	 if (cred->cr_uid == owner of vp) {
	     if	(mode &	VEXEC)
		 mask |= S_IXUSR;
	     if	(mode &	VREAD)
		 mask |= S_IRUSR;
	     if	(mode &	VWRITE)
		 mask |= S_IWUSR;
	     return (((mode of vp) & mask) == mask ? 0 : EACCES);
	 }

	 /* Otherwise, check the groups. */
	 for (i	= 0, gp	= cred->cr_groups; i < cred->cr_ngroups; i++, gp++)
	     if	(group of vp ==	*gp) {
		 if (mode & VEXEC)
		     mask |= S_IXGRP;
		 if (mode & VREAD)
		     mask |= S_IRGRP;
		 if (mode & VWRITE)
		     mask |= S_IWGRP;
		 return	(((mode	of vp) & mask) == mask ? 0 : EACCES);
	     }

	 /* Otherwise, check everyone else. */
	 if (mode & VEXEC)
	     mask |= S_IXOTH;
	 if (mode & VREAD)
	     mask |= S_IROTH;
	 if (mode & VWRITE)
	     mask |= S_IWOTH;
	 return	(((mode	of vp) & mask) == mask ? 0 : EACCES);
     }

ERRORS
     [EPERM]		An attempt was made to change an immutable file.

     [EACCES]		The permission bits the	file mode or the ACL do	not
			permit the requested access.

SEE ALSO
     vaccess(9), vaccess_acl_posix1e(9), vnode(9)

AUTHORS
     This man page was written by Doug Rabson.

BSD				 July 24, 1996				   BSD
NAME | SYNOPSIS | DESCRIPTION | LOCKS | RETURN VALUES | PSEUDOCODE | ERRORS | SEE ALSO | AUTHORS

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