blktap: Fix old QCow tapdisk image handling

When I tried to use QCow image, I found that only each second boot is
successful. As I discovered, this is caused by wrong handling old qcow
tapdisk images. Extended header flag is not stored correctly so the
blktap tries to change endian fo L1 table on each startup.

From: Miroslav Rezanina <mrezanin@redhat.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

diff --git a/tools/blktap/drivers/block-qcow.c b/tools/blktap/drivers/block-qcow.c
index 8027fcaca222d408ddf5e6f18cdeb45d19ee6581..0e4e9cfe0a5819882ba2d93cca1c7aa312d55180 100644 (file)
--- a/tools/blktap/drivers/block-qcow.c
+++ b/tools/blktap/drivers/block-qcow.c
@@ -862,11 +862,12 @@ static int tdqcow_open (struct disk_driver *dd, const char *name, td_flag_t flag
                be32_to_cpus(&exthdr->xmagic);
                if(exthdr->xmagic != XEN_MAGIC) 
                        goto end_xenhdr;
-    
+       
+               be32_to_cpus(&exthdr->flags);
                /* Try to detect old tapdisk images. They have to be fixed because 
                 * they don't use big endian but native endianess for the L1 table */
                if ((exthdr->flags & EXTHDR_L1_BIG_ENDIAN) == 0) {
-
+                       QCowHeader_ext *tmphdr = (QCowHeader_ext *)(buf2 + sizeof(QCowHeader));
                        /* 
                           The image is broken. Fix it. The L1 table has already been 
                           byte-swapped, so we can write it to the image file as it is
@@ -874,6 +875,11 @@ static int tdqcow_open (struct disk_driver *dd, const char *name, td_flag_t flag
                           for operation.
                         */
 
+                       /* Change ENDIAN flag and copy it to store buffer */
+                       exthdr->flags |= EXTHDR_L1_BIG_ENDIAN;
+                       tmphdr->flags = cpu_to_be32(exthdr->flags);
+
+
                        DPRINTF("qcow: Converting image to big endian L1 table\n");
 
                        memcpy(buf2 + s->l1_table_offset, s->l1_table, l1_table_size);
@@ -888,13 +894,6 @@ static int tdqcow_open (struct disk_driver *dd, const char *name, td_flag_t flag
                                cpu_to_be64s(&s->l1_table[i]);
                        }
 
-                       /* Write the big endian flag to the extended header */
-                       exthdr->flags |= EXTHDR_L1_BIG_ENDIAN;
-
-                       if (write(fd, buf, 512) != 512) {
-                               DPRINTF("qcow: Failed to write extended header\n");
-                               goto fail;
-                       }
                }
 
                /*Finally check the L1 table cksum*/
@@ -905,7 +904,6 @@ static int tdqcow_open (struct disk_driver *dd, const char *name, td_flag_t flag
                        goto end_xenhdr;
                        
                be32_to_cpus(&exthdr->min_cluster_alloc);
-               be32_to_cpus(&exthdr->flags);
                s->sparse = (exthdr->flags & SPARSE_FILE);
                s->min_cluster_alloc = exthdr->min_cluster_alloc; 
        }
@@ -1263,6 +1261,7 @@ int qcow_create(const char *filename, uint64_t total_size,
        } else
                flags = SPARSE_FILE;
 
+       flags |= EXTHDR_L1_BIG_ENDIAN;
        exthdr.flags = cpu_to_be32(flags);
        
        /* write all the data */