Expand cache= option and use write-through caching by default

This patch changes the cache= option to accept none, writeback, or writethough
to control the host page cache behavior.  By default, writethrough caching is
now used which internally is implemented by using O_DSYNC to open the disk
images.  When using -snapshot, writeback is used by default since data integrity
it not at all an issue.

cache=none has the same behavior as cache=off previously.  The later syntax is
still supported by now deprecated.  I also cleaned up the O_DIRECT
implementation to avoid many of the #ifdefs.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5485 c046a42c-6fe2-441c-8c8c-71466251a162

1 files changed, 12 insertions, 6 deletions

diff --git a/vl.c b/vl.c
index 97aca75179..c0e43ac030 100644
--- a/vl.c
+++ b/vl.c
@@ -5648,10 +5648,12 @@ static int drive_init(struct drive_opt *arg, int snapshot,
     }
 
     if (get_param_value(buf, sizeof(buf), "cache", str)) {
-        if (!strcmp(buf, "off"))
+        if (!strcmp(buf, "off") || !strcmp(buf, "none"))
             cache = 0;
-        else if (!strcmp(buf, "on"))
+        else if (!strcmp(buf, "writethrough"))
             cache = 1;
+        else if (!strcmp(buf, "writeback"))
+            cache = 2;
         else {
            fprintf(stderr, "qemu: invalid cache option\n");
            return -1;
@@ -5770,10 +5772,14 @@ static int drive_init(struct drive_opt *arg, int snapshot,
     if (!file[0])
         return 0;
     bdrv_flags = 0;
-    if (snapshot)
+    if (snapshot) {
         bdrv_flags |= BDRV_O_SNAPSHOT;
-    if (!cache)
-        bdrv_flags |= BDRV_O_DIRECT;
+        cache = 2; /* always use write-back with snapshot */
+    }
+    if (cache == 0) /* no caching */
+        bdrv_flags |= BDRV_O_NOCACHE;
+    else if (cache == 2) /* write-back */
+        bdrv_flags |= BDRV_O_CACHE_WB;
     if (bdrv_open2(bdrv, file, bdrv_flags, drv) < 0 || qemu_key_check(bdrv, file)) {
         fprintf(stderr, "qemu: could not open disk image %s\n",
                         file);
@@ -8145,7 +8151,7 @@ static void help(int exitcode)
            "-cdrom file     use 'file' as IDE cdrom image (cdrom is ide1 master)\n"
 	   "-drive [file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n"
            "       [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]\n"
-           "       [,cache=on|off][,format=f]\n"
+           "       [,cache=writethrough|writeback|none][,format=f]\n"
 	   "                use 'file' as a drive image\n"
            "-mtdblock file  use 'file' as on-board Flash memory image\n"
            "-sd file        use 'file' as SecureDigital card image\n"