VOP_ACCESS(9) BSD Kernel Developer's Manual VOP_ACCESS(9)NAMEVOP_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 proc *p);
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
p the process 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 proc *p)
{
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 file system.
*/
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] Permission denied
SEE ALSOvnode(9)AUTHORS
This man page was written by Doug Rabson.
BSD July 24, 1996 BSD
