Applied James McMechan's COW file creation speedup patch.

1 files changed, 21 insertions, 15 deletions

diff --git a/arch/um/drivers/ubd_user.c b/arch/um/drivers/ubd_user.c
index 93b6f3e..a756059 100644
--- a/arch/um/drivers/ubd_user.c
+++ b/arch/um/drivers/ubd_user.c
@@ -389,10 +389,10 @@ int create_cow_file(char *cow_file, char *backing_file, struct openflags flags,
 		    int sectorsize, int *bitmap_offset_out, 
 		    unsigned long *bitmap_len_out, int *data_offset_out)
 {
-	__u64 blocks;
-	long zero;
-	int err, fd, i;
+	__u64 offset;
+	int err, fd;
 	long long size;
+	char zero = 0;
 
 	flags.c = 1;
 	fd = open_ubd_file(cow_file, &flags, NULL, NULL, NULL, NULL, NULL);
@@ -406,22 +406,28 @@ int create_cow_file(char *cow_file, char *backing_file, struct openflags flags,
 	err = write_cow_header(cow_file, fd, backing_file, sectorsize, &size);
 	if(err) goto out_close;
 
-	blocks = (size + sectorsize - 1) / sectorsize;
-	blocks = (blocks + sizeof(long) * 8 - 1) / (sizeof(long) * 8);
-	zero = 0;
-	for(i = 0; i < blocks; i++){
-		err = write(fd, &zero, sizeof(zero));
-		if(err != sizeof(zero)){
-			printk("Write of bitmap to new COW file '%s' failed, "
-			       "errno = %d\n", cow_file, errno);
-			goto out_close;
-		}
-	}
-
 	sizes(size, sectorsize, sizeof(struct cow_header_v2), 
 	      bitmap_len_out, data_offset_out);
 	*bitmap_offset_out = sizeof(struct cow_header_v2);
 
+	offset = *data_offset_out + size - sizeof(zero);
+	err = os_seek_file(fd, offset);
+	if(err != 0){
+		printk("cow bitmap lseek failed : errno = %d\n", errno);
+		goto out_close;
+	}
+
+	/* does not really matter how much we write it is just to set EOF 
+	 * this also sets the entire COW bitmap
+	 * to zero without having to allocate it 
+	 */
+	err = os_write_file(fd, &zero, sizeof(zero));
+	if(err != sizeof(zero)){
+		printk("Write of bitmap to new COW file '%s' failed, "
+		       "errno = %d\n", cow_file, errno);
+		goto out_close;
+	}
+
 	return(fd);
 
  out_close: