From: David van Moolenbroek <david@minix3.org>
Date: Mon, 22 Jun 2015 11:50:04 +0000 (+0000)
Subject: libfsdriver: clear VM cache only if used
X-Git-Url: http://zhaoyanbai.com/repos/%22http:/www.isc.org/icons/zpipe.c?a=commitdiff_plain;h=refs%2Fchanges%2F07%2F3007%2F1;p=minix.git

libfsdriver: clear VM cache only if used

As part of its built-in mmap emulation support for "none" file system
services, libfsdriver clears the VM cache upon exit.  However, for
trivial file systems which do not even support reading from files, the
the VM cache need to be cleared either.  With this patch, the VM cache
is cleared only when modified, so that such trivial file systems need
not be given CLEARCACHE permission.

Change-Id: I518c092443455302b9b9728f10a3f894d2c8036b
---

diff --git a/minix/lib/libfsdriver/call.c b/minix/lib/libfsdriver/call.c
index 6b0e78ddb..f7bb9e50a 100644
--- a/minix/lib/libfsdriver/call.c
+++ b/minix/lib/libfsdriver/call.c
@@ -3,6 +3,8 @@
 #include <minix/ds.h>
 #include <sys/mman.h>
 
+static int fsdriver_vmcache;	/* have we used the VM cache? */
+
 /*
  * Process a READSUPER request from VFS.
  */
@@ -59,6 +61,7 @@ fsdriver_readsuper(const struct fsdriver * __restrict fdp,
 		fsdriver_mounted = TRUE;
 		fsdriver_device = dev;
 		fsdriver_root = root_node.fn_ino_nr;
+		fsdriver_vmcache = FALSE;
 	}
 
 	return r;
@@ -77,7 +80,7 @@ fsdriver_unmount(const struct fsdriver * __restrict fdp,
 		fdp->fdr_unmount();
 
 	/* If we used mmap emulation, clear any cached blocks from VM. */
-	if (fdp->fdr_peek == NULL && major(fsdriver_device) == NONE_MAJOR)
+	if (fsdriver_vmcache)
 		vm_clear_cache(fsdriver_device);
 
 	/* Update library-local state. */
@@ -256,6 +259,8 @@ builtin_peek(const struct fsdriver * __restrict fdp, ino_t ino_nr,
 		    pos, &flags, nbytes, VMSF_ONCE);
 
 		if (r == OK) {
+			fsdriver_vmcache = TRUE;
+
 			dev_off += nbytes;
 
 			r = nbytes;