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Re: [PATCH 2/6] block/vdi: Don't assume that blocks are larger than VdiH


From: Max Reitz
Subject: Re: [PATCH 2/6] block/vdi: Don't assume that blocks are larger than VdiHeader
Date: Wed, 24 Mar 2021 15:25:57 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0

On 17.03.21 19:00, Paolo Bonzini wrote:
From: David Edmondson <david.edmondson@oracle.com>

Given that the block size is read from the header of the VDI file, a
wide variety of sizes might be seen. Rather than re-using a block
sized memory region when writing the VDI header, allocate an
appropriately sized buffer.

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
Message-Id: <20210309144015.557477-3-david.edmondson@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
  block/vdi.c | 10 ++++++----
  1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/block/vdi.c b/block/vdi.c
index 2a6dc26124..548f8a057b 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -696,18 +696,20 @@ nonallocating_write:
if (block) {
          /* One or more new blocks were allocated. */
-        VdiHeader *header = (VdiHeader *) block;
+        VdiHeader *header;
          uint8_t *base;
          uint64_t offset;
          uint32_t n_sectors;
+ g_free(block);

This logic (checking @block != NULL) was a bit weird before and this just seems to accomodate it. We probably shouldn’t check @block, but some boolean, and *block should be freed after the while () loop.

Considering the “if (block)” was there already and it’d be weird to keep that check if *block were freed by that point, I suppose this isn’t making it worse, though, so:

Reviewed-by: Max Reitz <mreitz@redhat.com>

+        header = g_malloc(sizeof(*header));
+
          logout("now writing modified header\n");
          assert(VDI_IS_ALLOCATED(bmap_first));
          *header = s->header;
          vdi_header_to_le(header);
-        ret = bdrv_pwrite(bs->file, 0, block, sizeof(VdiHeader));
-        g_free(block);
-        block = NULL;
+        ret = bdrv_pwrite(bs->file, 0, header, sizeof(*header));
+        g_free(header);
if (ret < 0) {
              return ret;





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