NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

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

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

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

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

RETURN VALUES    [Toc]    [Back]

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

PSEUDOCODE    [Toc]    [Back]

     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    [Toc]    [Back]

     [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    [Toc]    [Back]

     vaccess(9), vaccess_acl_posix1e(9), vnode(9)

AUTHORS    [Toc]    [Back]

     This man page was written by Doug Rabson.


FreeBSD 5.2.1			 July 24, 1996			 FreeBSD 5.2.1