libext2fs: use a dynamically sized block zeroing buffer

Dynamically grow the block zeroing buffer to a maximum of 4MB, and
allow callers to provide their own zeroed buffer in
ext2fs_zero_blocks2().

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/lib/ext2fs/mkjournal.c b/lib/ext2fs/mkjournal.c
index e8f8b30..fcc6741 100644 (file)
--- a/lib/ext2fs/mkjournal.c
+++ b/lib/ext2fs/mkjournal.c
@@ -148,12 +148,13 @@ errfree:
  * attempt to free the static zeroizing buffer.  (This is to keep
  * programs that check for memory leaks happy.)
  */
-#define STRIDE_LENGTH (4194304 / fs->blocksize)
+#define MAX_STRIDE_LENGTH (4194304 / (int) fs->blocksize)
 errcode_t ext2fs_zero_blocks2(ext2_filsys fs, blk64_t blk, int num,
                              blk64_t *ret_blk, int *ret_count)
 {
        int             j, count;
-       static char     *buf;
+       static void     *buf;
+       static int      stride_length;
        errcode_t       retval;
 
        /* If fs is null, clean up the static buffer and return */
@@ -164,24 +165,36 @@ errcode_t ext2fs_zero_blocks2(ext2_filsys fs, blk64_t blk, int num,
                }
                return 0;
        }
+
+       /* Deal with zeroing less than 1 block */
+       if (num <= 0)
+               return 0;
+
        /* Allocate the zeroizing buffer if necessary */
-       if (!buf) {
-               buf = malloc(fs->blocksize * STRIDE_LENGTH);
-               if (!buf)
-                       return ENOMEM;
-               memset(buf, 0, fs->blocksize * STRIDE_LENGTH);
+       if (num > stride_length && stride_length < MAX_STRIDE_LENGTH) {
+               void *p;
+               int new_stride = num;
+
+               if (new_stride > MAX_STRIDE_LENGTH)
+                       new_stride = MAX_STRIDE_LENGTH;
+               p = realloc(buf, fs->blocksize * new_stride);
+               if (!p)
+                       return EXT2_ET_NO_MEMORY;
+               buf = p;
+               stride_length = new_stride;
+               memset(buf, 0, fs->blocksize * stride_length);
        }
        /* OK, do the write loop */
        j=0;
        while (j < num) {
-               if (blk % STRIDE_LENGTH) {
-                       count = STRIDE_LENGTH - (blk % STRIDE_LENGTH);
+               if (blk % stride_length) {
+                       count = stride_length - (blk % stride_length);
                        if (count > (num - j))
                                count = num - j;
                } else {
                        count = num - j;
-                       if (count > STRIDE_LENGTH)
-                               count = STRIDE_LENGTH;
+                       if (count > stride_length)
+                               count = stride_length;
                }
                retval = io_channel_write_blk64(fs->io, blk, count, buf);
                if (retval) {