[Libguestfs] [PATCH libnbd 1/3] copy: Allocate required size instead of maximum

[Nir Soffer]

If we cannot write zeroes efficiently, consider the command length when
allocating the buffer instead of allocating MAX_REQUEST_SIZE.

Signed-off-by: Nir Soffer <nsoffer at redhat.com>
---
 copy/multi-thread-copying.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/copy/multi-thread-copying.c b/copy/multi-thread-copying.c
index f86621b..b1cc9a5 100644
--- a/copy/multi-thread-copying.c
+++ b/copy/multi-thread-copying.c
@@ -501,6 +501,7 @@ static void
 fill_dst_range_with_zeroes (struct command *command)
 {
   char *data;
+  size_t data_size;
 
   if (destination_is_zero)
     goto free_and_return;
@@ -517,7 +518,8 @@ fill_dst_range_with_zeroes (struct command *command)
   /* Fall back to loop writing zeroes.  This is going to be slow
    * anyway, so do it synchronously. XXX
    */
-  data = calloc (1, MAX_REQUEST_SIZE);
+  data_size = MIN (MAX_REQUEST_SIZE, command->slice.len);
+  data = calloc (1, data_size);
   if (!data) {
     perror ("calloc");
     exit (EXIT_FAILURE);
@@ -525,8 +527,8 @@ fill_dst_range_with_zeroes (struct command *command)
   while (command->slice.len > 0) {
     size_t len = command->slice.len;
 
-    if (len > MAX_REQUEST_SIZE)
-      len = MAX_REQUEST_SIZE;
+    if (len > data_size)
+      len = data_size;
 
     dst->ops->synch_write (dst, data, len, command->offset);
     command->slice.len -= len;
-- 
2.26.2