From: Amjad Alsharafi <amjadsharafi10@gmail.com>
Date: Sat, 20 Jul 2024 10:13:30 +0000 (+0800)
Subject: vvfat: Fix bug in writing to middle of file
X-Git-Tag: qemu-xen-4.20.0~29^2~5
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=b881cf00c99e03bc8a3648581f97736ff275b18b;p=qemu-xen.git

vvfat: Fix bug in writing to middle of file

Before this commit, the behavior when calling `commit_one_file` for
example with `offset=0x2000` (second cluster), what will happen is that
we won't fetch the next cluster from the fat, and instead use the first
cluster for the read operation.

This is due to off-by-one error here, where `i=0x2000 !< offset=0x2000`,
thus not fetching the next cluster.

Signed-off-by: Amjad Alsharafi <amjadsharafi10@gmail.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <b97c1e1f1bc2f776061ae914f95d799d124fcd73.1721470238.git.amjadsharafi10@gmail.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---

diff --git a/block/vvfat.c b/block/vvfat.c
index 086fedf474..a67cfa823b 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -2525,8 +2525,9 @@ commit_one_file(BDRVVVFATState* s, int dir_index, uint32_t offset)
         return -1;
     }
 
-    for (i = s->cluster_size; i < offset; i += s->cluster_size)
+    for (i = 0; i < offset; i += s->cluster_size) {
         c = modified_fat_get(s, c);
+    }
 
     fd = qemu_open_old(mapping->path, O_RDWR | O_CREAT | O_BINARY, 0666);
     if (fd < 0) {