[Qemu-devel] [PATCH 04/32] vvfat: Do not clobber the user's geometry

[Markus Armbruster <armbru@redhat.com>]

vvfat creates a virtual VFAT filesystem with a certain logical
geometry that depends on its options.  It sets the "geometry hint" to
this geometry.  It is the only block driver to do this.

The geometry hint is about about *physical* geometry, and used only by
certain hard disk device models.

vvfat's hint is normally invisible for device models, because
bdrv_open() puts a raw format on top of vvfat's fat protocol.  That
raw format is where drive_init() puts the user's geometry (if any),
and where the device model gets it from.

Nobody complained, because the default physical geometry is the same
as vvfat's logical geometry:

    opts        LCHS        def. PCHS
                1024,16,63  same
    :32:        1024,16,63  same
    :16:        1024,16,63  same
    :12:          64,16,63  same

Except when you specify :floppy:

    opts        LCHS        def. PCHS
       :floppy:   80, 2,36  5,16,63
    :32:floppy:   80, 2,36  5,16,63
    :16:floppy:   80, 2,36  5,16,63
    :12:floppy:   80, 2,18  2,16,63

Silly thing to do for use with a hard disk.

However, the "raw" format can be suppressed by adding an
redundant-looking "format=vvfat" to "file=fat:FOO".  Then, vvfat's
hint clobbers the user's geometry, i.e. -drive options cyls, heads,
secs get silently ignored.  Don't do that.

No change without format=vvfat.  With it, the user's hard disk
geometry (-drive options cyls, heads, secs) is now obeyed, and the
default hard disk geometry with :floppy: now matches the one without
format=vvfat.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 block/vvfat.c |   52 ++++++++++++++++++++++++++++------------------------
 1 files changed, 28 insertions(+), 24 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index e2b83a2..07d637b 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -359,11 +359,12 @@ typedef struct BDRVVVFATState {
  * if the position is outside the specified geometry, fill maximum value for CHS
  * and return 1 to signal overflow.
  */
-static int sector2CHS(BlockDriverState* bs, mbr_chs_t * chs, int spos){
+static int sector2CHS(mbr_chs_t *chs, int spos, int cyls, int heads, int secs)
+{
     int head,sector;
-    sector   = spos % (bs->secs);  spos/= bs->secs;
-    head     = spos % (bs->heads); spos/= bs->heads;
-    if(spos >= bs->cyls){
+    sector   = spos % secs;  spos /= secs;
+    head     = spos % heads; spos /= heads;
+    if (spos >= cyls) {
         /* Overflow,
         it happens if 32bit sector positions are used, while CHS is only 24bit.
         Windows/Dos is said to take 1023/255/63 as nonrepresentable CHS */
@@ -378,7 +379,7 @@ static int sector2CHS(BlockDriverState* bs, mbr_chs_t * chs, int spos){
     return 0;
 }
 
-static void init_mbr(BDRVVVFATState* s)
+static void init_mbr(BDRVVVFATState *s, int cyls, int heads, int secs)
 {
     /* TODO: if the files mbr.img and bootsect.img exist, use them */
     mbr_t* real_mbr=(mbr_t*)s->first_sectors;
@@ -393,8 +394,10 @@ static void init_mbr(BDRVVVFATState* s)
     partition->attributes=0x80; /* bootable */
 
     /* LBA is used when partition is outside the CHS geometry */
-    lba = sector2CHS(s->bs, &partition->start_CHS, s->first_sectors_number-1);
-    lba |= sector2CHS(s->bs, &partition->end_CHS, s->bs->total_sectors - 1);
+    lba  = sector2CHS(&partition->start_CHS, s->first_sectors_number - 1,
+                     cyls, heads, secs);
+    lba |= sector2CHS(&partition->end_CHS,   s->bs->total_sectors - 1,
+                     cyls, heads, secs);
 
     /*LBA partitions are identified only by start/length_sector_long not by CHS*/
     partition->start_sector_long  = cpu_to_le32(s->first_sectors_number - 1);
@@ -831,7 +834,7 @@ static inline off_t cluster2sector(BDRVVVFATState* s, uint32_t cluster_num)
 }
 
 static int init_directories(BDRVVVFATState* s,
-	const char* dirname)
+                            const char *dirname, int heads, int secs)
 {
     bootsector_t* bootsector;
     mapping_t* mapping;
@@ -958,8 +961,8 @@ static int init_directories(BDRVVVFATState* s,
     bootsector->media_type=(s->first_sectors_number>1?0xf8:0xf0); /* media descriptor (f8=hd, f0=3.5 fd)*/
     s->fat.pointer[0] = bootsector->media_type;
     bootsector->sectors_per_fat=cpu_to_le16(s->sectors_per_fat);
-    bootsector->sectors_per_track=cpu_to_le16(s->bs->secs);
-    bootsector->number_of_heads=cpu_to_le16(s->bs->heads);
+    bootsector->sectors_per_track = cpu_to_le16(secs);
+    bootsector->number_of_heads = cpu_to_le16(heads);
     bootsector->hidden_sectors=cpu_to_le32(s->first_sectors_number==1?0:0x3f);
     bootsector->total_sectors=cpu_to_le32(s->sector_count>0xffff?s->sector_count:0);
 
@@ -992,7 +995,7 @@ static void vvfat_rebind(BlockDriverState *bs)
 static int vvfat_open(BlockDriverState *bs, const char* dirname, int flags)
 {
     BDRVVVFATState *s = bs->opaque;
-    int i;
+    int i, cyls, heads, secs;
 
 #ifdef DEBUG
     vvv = s;
@@ -1034,24 +1037,28 @@ DLOG(if (stderr == NULL) {
 	/* 1.44MB or 2.88MB floppy.  2.88MB can be FAT12 (default) or FAT16. */
 	if (!s->fat_type) {
 	    s->fat_type = 12;
-	    bs->secs = 36;
+            secs = 36;
 	    s->sectors_per_cluster=2;
 	} else {
-	    bs->secs=(s->fat_type == 12 ? 18 : 36);
+            secs = s->fat_type == 12 ? 18 : 36;
 	    s->sectors_per_cluster=1;
 	}
 	s->first_sectors_number = 1;
-	bs->cyls=80; bs->heads=2;
+        cyls = 80;
+        heads = 2;
     } else {
 	/* 32MB or 504MB disk*/
 	if (!s->fat_type) {
 	    s->fat_type = 16;
 	}
-	bs->cyls=(s->fat_type == 12 ? 64 : 1024);
-	bs->heads=16; bs->secs=63;
+        cyls = s->fat_type == 12 ? 64 : 1024;
+        heads = 16;
+        secs = 63;
     }
+    fprintf(stderr, "vvfat %s chs %d,%d,%d\n",
+            dirname, cyls, heads, secs);
 
-    s->sector_count=bs->cyls*bs->heads*bs->secs-(s->first_sectors_number-1);
+    s->sector_count = cyls * heads * secs - (s->first_sectors_number - 1);
 
     if (strstr(dirname, ":rw:")) {
 	if (enable_write_target(s))
@@ -1067,19 +1074,16 @@ DLOG(if (stderr == NULL) {
     else
 	dirname += i+1;
 
-    bs->total_sectors=bs->cyls*bs->heads*bs->secs;
+    bs->total_sectors = cyls * heads * secs;
 
-    if(init_directories(s, dirname))
+    if (init_directories(s, dirname, heads, secs)) {
 	return -1;
+    }
 
     s->sector_count = s->faked_sectors + s->sectors_per_cluster*s->cluster_count;
 
     if(s->first_sectors_number==0x40)
-	init_mbr(s);
-    else {
-        /* MS-DOS does not like to know about CHS (?). */
-	bs->heads = bs->cyls = bs->secs = 0;
-    }
+        init_mbr(s, cyls, heads, secs);
 
     //    assert(is_consistent(s));
     qemu_co_mutex_init(&s->lock);
-- 
1.7.6.5