[PATCH v20210701 19/40] tools: save: move iov array

[Olaf Hering <olaf@xxxxxxxxx>]

Remove allocation from hotpath, move iov array into preallocated space.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
---
 tools/libs/saverestore/common.h | 2 ++
 tools/libs/saverestore/save.c   | 7 ++-----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/tools/libs/saverestore/common.h b/tools/libs/saverestore/common.h
index 25ee8fcb0f..c8a30acf7b 100644
--- a/tools/libs/saverestore/common.h
+++ b/tools/libs/saverestore/common.h
@@ -231,6 +231,8 @@ struct sr_save_arrays {
     xen_pfn_t types[MAX_BATCH_SIZE];
     /* write_batch: Errors from attempting to map the gfns. */
     int errors[MAX_BATCH_SIZE];
+    /* write_batch: iovec[] for writev(). */
+    struct iovec iov[MAX_BATCH_SIZE + 4];
 };
 
 struct sr_restore_arrays {
diff --git a/tools/libs/saverestore/save.c b/tools/libs/saverestore/save.c
index 9ebbf00ce7..1a5f3d29ea 100644
--- a/tools/libs/saverestore/save.c
+++ b/tools/libs/saverestore/save.c
@@ -97,7 +97,7 @@ static int write_batch(struct xc_sr_context *ctx)
     unsigned int nr_pfns = ctx->save.nr_batch_pfns;
     void *page, *orig_page;
     uint64_t *rec_pfns = NULL;
-    struct iovec *iov = NULL; int iovcnt = 0;
+    struct iovec *iov = ctx->save.m->iov; int iovcnt = 0;
     struct xc_sr_rec_page_data_header hdr = { 0 };
     struct xc_sr_record rec = {
         .type = REC_TYPE_PAGE_DATA,
@@ -109,10 +109,8 @@ static int write_batch(struct xc_sr_context *ctx)
     guest_data = calloc(nr_pfns, sizeof(*guest_data));
     /* Pointers to locally allocated pages.  Need freeing. */
     local_pages = calloc(nr_pfns, sizeof(*local_pages));
-    /* iovec[] for writev(). */
-    iov = malloc((nr_pfns + 4) * sizeof(*iov));
 
-    if ( !guest_data || !local_pages || !iov )
+    if ( !guest_data || !local_pages )
     {
         ERROR("Unable to allocate arrays for a batch of %u pages",
               nr_pfns);
@@ -266,7 +264,6 @@ static int write_batch(struct xc_sr_context *ctx)
         xenforeignmemory_unmap(xch->fmem, guest_mapping, nr_pages_mapped);
     for ( i = 0; local_pages && i < nr_pfns; ++i )
         free(local_pages[i]);
-    free(iov);
     free(local_pages);
     free(guest_data);