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[PATCH 1/2] vvfat: allow some writes to bootsector
From: |
Hervé Poussineau |
Subject: |
[PATCH 1/2] vvfat: allow some writes to bootsector |
Date: |
Sat, 3 Sep 2022 18:23:01 +0200 |
'reserved1' field in bootsector is used to mark volume dirty, or need to verify.
Allow writes to bootsector which only changes the 'reserved1' field.
This fixes I/O errors on Windows guests.
Resolves: https://bugs.launchpad.net/qemu/+bug/1889421
Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
---
block/vvfat.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/block/vvfat.c b/block/vvfat.c
index d6dd919683d..35057a51c67 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -2993,11 +2993,27 @@ DLOG(checkpoint());
vvfat_close_current_file(s);
+ if (sector_num == s->offset_to_bootsector && nb_sectors == 1) {
+ /*
+ * Write on bootsector. Allow only changing the reserved1 field,
+ * used to mark volume dirtiness
+ */
+ const unsigned char *initial = s->first_sectors
+ + s->offset_to_bootsector * 0x200;
+ for (i = 0; i < 0x200; i++) {
+ if (i != offsetof(bootsector_t, u.fat16.reserved1) &&
+ initial[i] != buf[i]) {
+ fprintf(stderr, "Tried to write to protected bootsector\n");
+ return -1;
+ }
+ }
+ return 0;
+ }
+
/*
* Some sanity checks:
* - do not allow writing to the boot sector
*/
-
if (sector_num < s->offset_to_fat)
return -1;
--
2.36.2