[src/trunk]: src/sys/kern do_posix_fadvise: fix and improve previous change -...

[rmind <rmind%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/be62427f5dac
branches:  trunk
changeset: 759850:be62427f5dac
user:      rmind <rmind%NetBSD.org@localhost>
date:      Sat Dec 18 01:18:48 2010 +0000

description:
do_posix_fadvise: fix and improve previous change - add a comment with
some rationale and handle few range overflows.

Per report/discussion with yamt@.

diffstat:

 sys/kern/sys_descrip.c |  26 +++++++++++++++++++-------
 1 files changed, 19 insertions(+), 7 deletions(-)

diffs (55 lines):

diff -r a234717a3cd4 -r be62427f5dac sys/kern/sys_descrip.c
--- a/sys/kern/sys_descrip.c    Sat Dec 18 01:13:36 2010 +0000
+++ b/sys/kern/sys_descrip.c    Sat Dec 18 01:18:48 2010 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sys_descrip.c,v 1.18 2010/10/27 02:58:04 rmind Exp $   */
+/*     $NetBSD: sys_descrip.c,v 1.19 2010/12/18 01:18:48 rmind Exp $   */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -67,7 +67,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_descrip.c,v 1.18 2010/10/27 02:58:04 rmind Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_descrip.c,v 1.19 2010/12/18 01:18:48 rmind Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -662,9 +662,8 @@
        case POSIX_FADV_NORMAL:
        case POSIX_FADV_RANDOM:
        case POSIX_FADV_SEQUENTIAL:
-
                /*
-                * We ignore offset and size.  must lock the file to
+                * We ignore offset and size.  Must lock the file to
                 * do this, as f_advice is sub-word sized.
                 */
                mutex_enter(&fp->f_lock);
@@ -680,9 +679,22 @@
 
        case POSIX_FADV_DONTNEED:
                vp = fp->f_data;
-               mutex_enter(&vp->v_interlock);
-               error = VOP_PUTPAGES(vp, trunc_page(offset),
-                   round_page(endoffset), PGO_DEACTIVATE | PGO_CLEANIT);
+               /*
+                * Align the region to page boundaries as VOP_PUTPAGES expects
+                * by shrinking it.  We shrink instead of expand because we
+                * do not want to deactivate cache outside of the requested
+                * region.  It means that if the specified region is smaller
+                * than PAGE_SIZE, we do nothing.
+                */
+               if (round_page(offset) < trunc_page(endoffset) &&
+                   offset <= round_page(offset)) {
+                       mutex_enter(&vp->v_interlock);
+                       error = VOP_PUTPAGES(vp,
+                           round_page(offset), trunc_page(endoffset),
+                           PGO_DEACTIVATE | PGO_CLEANIT);
+               } else {
+                       error = 0;
+               }
                break;
 
        case POSIX_FADV_NOREUSE: