[PATCH v2 0/2] Fix some problems with vvfat in R/W mode

[PATCH v2 0/2] Fix some problems with vvfat in R/W mode

[Hervé Poussineau]

Hi,

When testing vvfat in read-write mode, I came across some blocking
problems when using Windows guests.
This patchset is not here to fix all problems of vvfat, but only the
main ones I encountered.

First patch allows setting/resetting the 'volume dirty' flag on
boosector, and the second one allows creating file names with spaces.

Hervé

Changes since v1:
- updated patch 1 with remarks (modify in-memory copy, add comment about
  FAT32)

Hervé Poussineau (2):
  vvfat: allow some writes to bootsector
  vvfat: allow spaces in file names

 block/vvfat.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

-- 
2.36.2

[PATCH v2 1/2] vvfat: allow some writes to bootsector

[Hervé Poussineau]

'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 | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index d6dd919683d..ae53f0d7283 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -2993,11 +2993,35 @@ 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
+         */
+        unsigned char *bootsector = s->first_sectors
+                                    + s->offset_to_bootsector * 0x200;
+        /*
+         * LATER TODO: if FAT32, this is wrong (see init_directories(),
+         * which always creates a FAT16 bootsector)
+         */
+        const int reserved1_offset = offsetof(bootsector_t, u.fat16.reserved1);
+
+        for (i = 0; i < 0x200; i++) {
+            if (i != reserved1_offset && bootsector[i] != buf[i]) {
+                fprintf(stderr, "Tried to write to protected bootsector\n");
+                return -1;
+            }
+        }
+
+        /* Update bootsector with the only updatable byte, and return success */
+        bootsector[reserved1_offset] = buf[reserved1_offset];
+        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

[PATCH v2 2/2] vvfat: allow spaces in file names

[Hervé Poussineau]

In R/W mode, files with spaces were never created on host side.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1176
Fixes: c79e243ed67683d6d06692bd7040f7394da178b0
Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
---
 block/vvfat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index ae53f0d7283..392eab5168b 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -499,7 +499,7 @@ static bool valid_filename(const unsigned char *name)
               (c >= 'A' && c <= 'Z') ||
               (c >= 'a' && c <= 'z') ||
               c > 127 ||
-              strchr("$%'-_@~`!(){}^#&.+,;=[]", c) != NULL))
+              strchr(" $%'-_@~`!(){}^#&.+,;=[]", c) != NULL))
         {
             return false;
         }
-- 
2.36.2

Re: [PATCH v2 0/2] Fix some problems with vvfat in R/W mode

[Kevin Wolf]

Am 10.10.2022 um 19:55 hat Hervé Poussineau geschrieben:
> Hi,
> 
> When testing vvfat in read-write mode, I came across some blocking
> problems when using Windows guests.
> This patchset is not here to fix all problems of vvfat, but only the
> main ones I encountered.
> 
> First patch allows setting/resetting the 'volume dirty' flag on
> boosector, and the second one allows creating file names with spaces.
> 
> Hervé
> 
> Changes since v1:
> - updated patch 1 with remarks (modify in-memory copy, add comment about
>   FAT32)

Thanks, applied to the block branch.

Kevin