[Qemu-devel] [PATCH 4/9] Remove 4 MB stack frame usage from sheepdog

["Daniel P. Berrange" <berrange@redhat.com>]

From: "Daniel P. Berrange" <berrange@redhat.com>

The sheepdog driver declares an instance of BDRVSheepdogState
in the stack. This struct is 4 MB in size. While the default
Linux stack size may be 10 MB, we should not assume that since
QEMU needs to be portable to other OS.

block/sheepdog.c: In function ‘sd_create’:
block/sheepdog.c:1240:1: error: the frame size of 4199888 bytes is larger than 131072 bytes [-Werror=frame-larger-than=]

* block/sheepdog.c: Allow BDRVSheepdogState on the heap
  instead of stack
* configure: Add -Wframe-larger-than to validate stack
  size does not exceed 128k

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 block/sheepdog.c |   43 ++++++++++++++++++++++++++-----------------
 configure        |    1 +
 2 files changed, 27 insertions(+), 17 deletions(-)

diff --git a/block/sheepdog.c b/block/sheepdog.c
index 00276f6f..ff6f3d2 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -1163,20 +1163,22 @@ static int sd_create(const char *filename, QEMUOptionParameter *options)
     uint32_t vid = 0, base_vid = 0;
     int64_t vdi_size = 0;
     char *backing_file = NULL;
-    BDRVSheepdogState s;
+    BDRVSheepdogState *s1;
     char vdi[SD_MAX_VDI_LEN], tag[SD_MAX_VDI_TAG_LEN];
     uint32_t snapid;
     int prealloc = 0;
     const char *vdiname;
+    int rv = -EINVAL;
+
+    s1 = g_new0(BDRVSheepdogState, 1);
 
     strstart(filename, "sheepdog:", &vdiname);
 
-    memset(&s, 0, sizeof(s));
     memset(vdi, 0, sizeof(vdi));
     memset(tag, 0, sizeof(tag));
-    if (parse_vdiname(&s, vdiname, vdi, &snapid, tag) < 0) {
+    if (parse_vdiname(s1, vdiname, vdi, &snapid, tag) < 0) {
         error_report("invalid filename");
-        return -EINVAL;
+        goto cleanup;
     }
 
     while (options && options->name) {
@@ -1192,7 +1194,7 @@ static int sd_create(const char *filename, QEMUOptionParameter *options)
             } else {
                 error_report("Invalid preallocation mode: '%s'",
                              options->value.s);
-                return -EINVAL;
+                goto cleanup;
             }
         }
         options++;
@@ -1200,43 +1202,50 @@ static int sd_create(const char *filename, QEMUOptionParameter *options)
 
     if (vdi_size > SD_MAX_VDI_SIZE) {
         error_report("too big image size");
-        return -EINVAL;
+        goto cleanup;
     }
 
     if (backing_file) {
         BlockDriverState *bs;
-        BDRVSheepdogState *s;
+        BDRVSheepdogState *s2;
         BlockDriver *drv;
 
         /* Currently, only Sheepdog backing image is supported. */
         drv = bdrv_find_protocol(backing_file);
         if (!drv || strcmp(drv->protocol_name, "sheepdog") != 0) {
             error_report("backing_file must be a sheepdog image");
-            return -EINVAL;
+            goto cleanup;
         }
 
         ret = bdrv_file_open(&bs, backing_file, 0);
-        if (ret < 0)
-            return -EIO;
+        if (ret < 0) {
+            rv = -EIO;
+            goto cleanup;
+        }
 
-        s = bs->opaque;
+        s2 = bs->opaque;
 
-        if (!is_snapshot(&s->inode)) {
+        if (!is_snapshot(&s2->inode)) {
             error_report("cannot clone from a non snapshot vdi");
             bdrv_delete(bs);
-            return -EINVAL;
+            goto cleanup;
         }
 
-        base_vid = s->inode.vdi_id;
+        base_vid = s2->inode.vdi_id;
         bdrv_delete(bs);
     }
 
-    ret = do_sd_create(vdi, vdi_size, base_vid, &vid, 0, s.addr, s.port);
+    ret = do_sd_create(vdi, vdi_size, base_vid, &vid, 0, s1->addr, s1->port);
     if (!prealloc || ret) {
-        return ret;
+        rv = ret;
+        goto cleanup;
     }
 
-    return sd_prealloc(filename);
+    rv = sd_prealloc(filename);
+
+ cleanup:
+    g_free(s1);
+    return rv;
 }
 
 static void sd_close(BlockDriverState *bs)
diff --git a/configure b/configure
index 44b28c8..28b5dd5 100755
--- a/configure
+++ b/configure
@@ -1165,6 +1165,7 @@ gcc_flags="$gcc_flags -Wmissing-include-dirs"
 gcc_flags="$gcc_flags -Wempty-body"
 gcc_flags="$gcc_flags -Wnested-externs"
 gcc_flags="$gcc_flags -Wendif-labels"
+gcc_flags="$gcc_flags -Wframe-larger-than=131072"
 cat > $TMPC << EOF
 int main(void) { return 0; }
 EOF
-- 
1.7.7.6