Am 03.09.2022 um 18:23 hat Hervé Poussineau geschrieben:
> '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 <hpous...@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) &&
I think you need to check the FAT version (s->fat_type) before accessing
u.fat16. For FAT32, the "reserved" field is at a different offset (but
seems to have the same meaning).
> + initial[i] != buf[i]) {
> + fprintf(stderr, "Tried to write to protected bootsector\n");
> + return -1;
> + }
> + }
> + return 0;
> + }
Should we update s->first_sectors with the new value so that the guest
would actually read back what it wrote instead of having the change
disappear magically?
> /*
> * Some sanity checks:
> * - do not allow writing to the boot sector
> */
> -
> if (sector_num < s->offset_to_fat)
> return -1;
Kevin
