[Qemu-devel] Wipe patch

* [Qemu-devel] Wipe patch
@ 2006-07-26  8:23 ZIGLIO, Frediano, VF-IT
  2006-07-26  8:41 ` Brad Campbell
  2006-08-02  2:25 ` Brad Campbell
  0 siblings, 2 replies; 14+ messages in thread
From: ZIGLIO, Frediano, VF-IT @ 2006-07-26  8:23 UTC (permalink / raw)
  To: qemu-devel

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Hi,
  well, this is not a definitive patch but it works. The aim is to be
able to wipe the disk without allocating entire space. When you wipe a
disk the program fill disk with zero bytes so disk image increase to
allocate all space. This just patch detect null byte writes and do not
write all zero byte clusters.

Frediano Ziglio


[-- Attachment #2: wipe.diff --]
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Index: block-qcow.c
===================================================================
RCS file: /sources/qemu/qemu/block-qcow.c,v
retrieving revision 1.7
diff -u -1 -0 -r1.7 block-qcow.c

--- block-qcow.c	4 Jun 2006 11:39:06 -0000	1.7
+++ block-qcow.c	26 Jul 2006 07:15:17 -0000
@@ -480,47 +480,77 @@
                                 &s->aes_decrypt_key);
             }
         }
         nb_sectors -= n;
         sector_num += n;
         buf += n * 512;
     }
     return 0;
 }
 
+static int is_not_zero(const uint8_t *data, int len)
+{
+    int left;
+    while (len && (((unsigned int) data) & 3) != 0) {
+        if (*data++)
+            return 1;
+        --len;
+    }
+    left = len & 3;
+    len >>= 2;
+    while (len) {
+        if (*((uint32_t *)data) != 0)
+            return 1;
+        data += 4;
+        --len;
+    }
+    while (left) {
+        if (*data++)
+            return 1;
+        --left;
+    }
+    return 0;
+}
+
 static int qcow_write(BlockDriverState *bs, int64_t sector_num, 
                      const uint8_t *buf, int nb_sectors)
 {
     BDRVQcowState *s = bs->opaque;
     int ret, index_in_cluster, n;
     uint64_t cluster_offset;
+    int not_zero;
     
     while (nb_sectors > 0) {
         index_in_cluster = sector_num & (s->cluster_sectors - 1);
         n = s->cluster_sectors - index_in_cluster;
         if (n > nb_sectors)
             n = nb_sectors;
-        cluster_offset = get_cluster_offset(bs, sector_num << 9, 1, 0, 
+        not_zero = is_not_zero(buf, n * 512);
+        cluster_offset = get_cluster_offset(bs, sector_num << 9, not_zero, 0, 
                                             index_in_cluster, 
                                             index_in_cluster + n);
-        if (!cluster_offset)
-            return -1;
+        if (!cluster_offset) {
+            if (not_zero)
+                return -1;
+            goto next_cluster;
+        }
         lseek(s->fd, cluster_offset + index_in_cluster * 512, SEEK_SET);
         if (s->crypt_method) {
             encrypt_sectors(s, sector_num, s->cluster_data, buf, n, 1,
                             &s->aes_encrypt_key);
             ret = write(s->fd, s->cluster_data, n * 512);
         } else {
             ret = write(s->fd, buf, n * 512);
         }
         if (ret != n * 512) 
             return -1;
+next_cluster:
         nb_sectors -= n;
         sector_num += n;
         buf += n * 512;
     }
     s->cluster_cache_offset = -1; /* disable compressed cache */
     return 0;
 }
 
 static void qcow_close(BlockDriverState *bs)
 {

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