backends/hostmem-file: Allow to specify full pathname for backing file

This allows to explicitly specify file name to use with the backend. This
is important when using it together with ivshmem in order to make it backed
by hugetlbfs. By default filename is autogenerated using mkstemp(), and the
file is unlink()ed after creation, effectively making it anonymous. This is
not very useful with ivshmem because it ends up in a memory which cannot be
accessed by something else.

Distinction between directory and file name is done by stat() check. If an
existing directory is given, the code keeps old behavior. Otherwise it
creates or opens a file with the given pathname.

Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
Tested-by: Igor Skalkin <i.skalkin@samsung.com>
Message-Id: <004301d11166$9672fe30$c358fa90$@samsung.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 21 insertions, 13 deletions

diff --git a/exec.c b/exec.c
index 819ecc3d64..1e8b51b48b 100644
--- a/exec.c
+++ b/exec.c
@@ -1205,6 +1205,7 @@ static void *file_ram_alloc(RAMBlock *block,
                             const char *path,
                             Error **errp)
 {
+    struct stat st;
     char *filename;
     char *sanitized_name;
     char *c;
@@ -1233,26 +1234,33 @@ static void *file_ram_alloc(RAMBlock *block,
         goto error;
     }
 
-    /* Make name safe to use with mkstemp by replacing '/' with '_'. */
-    sanitized_name = g_strdup(memory_region_name(block->mr));
-    for (c = sanitized_name; *c != '\0'; c++) {
-        if (*c == '/')
-            *c = '_';
-    }
+    if (!stat(path, &st) && S_ISDIR(st.st_mode)) {
+        /* Make name safe to use with mkstemp by replacing '/' with '_'. */
+        sanitized_name = g_strdup(memory_region_name(block->mr));
+        for (c = sanitized_name; *c != '\0'; c++) {
+            if (*c == '/') {
+                *c = '_';
+            }
+        }
 
-    filename = g_strdup_printf("%s/qemu_back_mem.%s.XXXXXX", path,
-                               sanitized_name);
-    g_free(sanitized_name);
+        filename = g_strdup_printf("%s/qemu_back_mem.%s.XXXXXX", path,
+                                   sanitized_name);
+        g_free(sanitized_name);
+
+        fd = mkstemp(filename);
+        if (fd >= 0) {
+            unlink(filename);
+        }
+        g_free(filename);
+    } else {
+        fd = open(path, O_RDWR | O_CREAT, 0644);
+    }
 
-    fd = mkstemp(filename);
     if (fd < 0) {
         error_setg_errno(errp, errno,
                          "unable to create backing store for hugepages");
-        g_free(filename);
         goto error;
     }
-    unlink(filename);
-    g_free(filename);
 
     memory = ROUND_UP(memory, hpagesize);