[PULL,10/13] vvfat: Fix wrong checks for cluster mappings invariant

Commit Message

Kevin Wolf Aug. 5, 2024, 9:08 p.m. UTC

From: Amjad Alsharafi <[e-mail]>

How this `abort` was intended to check for was:
- if the `mapping->first_mapping_index` is not the same as
  `first_mapping_index`, which **should** happen only in one case,
  when we are handling the first mapping, in that case
  `mapping->first_mapping_index == -1`, in all other cases, the other
  mappings after the first should have the condition `true`.
- From above, we know that this is the first mapping, so if the offset
  is not `0`, then abort, since this is an invalid state.

The issue was that `first_mapping_index` is not set if we are
checking from the middle, the variable `first_mapping_index` is
only set if we passed through the check `cluster_was_modified` with the
first mapping, and in the same function call we checked the other
mappings.

One approach is to go into the loop even if `cluster_was_modified`
is not true so that we will be able to set `first_mapping_index` for the
first mapping, but since `first_mapping_index` is only used here,
another approach is to just check manually for the
`mapping->first_mapping_index != -1` since we know that this is the
value for the only entry where `offset == 0` (i.e. first mapping).

Signed-off-by: Amjad Alsharafi <[e-mail]>
Reviewed-by: Kevin Wolf <[e-mail]>
Message-ID: <b0fbca[e-mail]>
Signed-off-by: Kevin Wolf <[e-mail]>
---
 block/vvfat.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

Patch

diff --git a/block/vvfat.c b/block/vvfat.c
index cfde468c2e..e3a83fbc88 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1880,7 +1880,6 @@  get_cluster_count_for_direntry(BDRVVVFATState* s, direntry_t* direntry, const ch
 
     uint32_t cluster_num = begin_of_direntry(direntry);
     uint32_t offset = 0;
-    int first_mapping_index = -1;
     mapping_t* mapping = NULL;
     const char* basename2 = NULL;
 
@@ -1942,14 +1941,9 @@  get_cluster_count_for_direntry(BDRVVVFATState* s, direntry_t* direntry, const ch
 
                         if (strcmp(basename, basename2))
                             copy_it = 1;
-                        first_mapping_index = array_index(&(s->mapping), mapping);
-                    }
-
-                    if (mapping->first_mapping_index != first_mapping_index
-                            && mapping->info.file.offset > 0) {
-                        abort();
-                        copy_it = 1;
                     }
+                    assert(mapping->first_mapping_index == -1
+                            || mapping->info.file.offset > 0);
 
                     /* need to write out? */
                     if (!was_modified && is_file(direntry)) {