[Qemu-devel] [PATCH v5 1/6] memfd: split qemu_memfd_alloc()

[Marc-André Lureau]

Add a function to only create a memfd, without mmap. The function is
used in the following memory backend.

Signed-off-by: Marc-André Lureau <address@hidden>
---
 include/qemu/memfd.h |  1 +
 util/memfd.c         | 61 +++++++++++++++++++++++++++++++---------------------
 2 files changed, 37 insertions(+), 25 deletions(-)

diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
index 745a8c501e..41c24d807c 100644
--- a/include/qemu/memfd.h
+++ b/include/qemu/memfd.h
@@ -16,6 +16,7 @@
 #define F_SEAL_WRITE    0x0008  /* prevent writes */
 #endif
 
+int qemu_memfd_create(const char *name, size_t size, unsigned int seals);
 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
                        int *fd);
 void qemu_memfd_free(void *ptr, size_t size, int fd);
diff --git a/util/memfd.c b/util/memfd.c
index 4571d1aba8..e9c1a0e700 100644
--- a/util/memfd.c
+++ b/util/memfd.c
@@ -55,6 +55,38 @@ static int memfd_create(const char *name, unsigned int flags)
 #define MFD_ALLOW_SEALING 0x0002U
 #endif
 
+int qemu_memfd_create(const char *name, size_t size, unsigned int seals)
+{
+    int mfd = -1;
+
+#ifdef CONFIG_LINUX
+    unsigned int flags = MFD_CLOEXEC;
+
+    if (seals) {
+        flags |= MFD_ALLOW_SEALING;
+    }
+
+    mfd = memfd_create(name, flags);
+    if (mfd < 0) {
+        return -1;
+    }
+
+    if (ftruncate(mfd, size) == -1) {
+        perror("ftruncate");
+        close(mfd);
+        return -1;
+    }
+
+    if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
+        perror("fcntl");
+        close(mfd);
+        return -1;
+    }
+#endif
+
+    return mfd;
+}
+
 /*
  * This is a best-effort helper for shared memory allocation, with
  * optional sealing. The helper will do his best to allocate using
@@ -65,35 +97,14 @@ void *qemu_memfd_alloc(const char *name, size_t size, 
unsigned int seals,
                        int *fd)
 {
     void *ptr;
-    int mfd = -1;
-
-    *fd = -1;
-
-#ifdef CONFIG_LINUX
-    if (seals) {
-        mfd = memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
-    }
+    int mfd = qemu_memfd_create(name, size, seals);
 
+    /* some systems have memfd without sealing */
     if (mfd == -1) {
-        /* some systems have memfd without sealing */
-        mfd = memfd_create(name, MFD_CLOEXEC);
-        seals = 0;
+        mfd = qemu_memfd_create(name, size, 0);
     }
-#endif
-
-    if (mfd != -1) {
-        if (ftruncate(mfd, size) == -1) {
-            perror("ftruncate");
-            close(mfd);
-            return NULL;
-        }
 
-        if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
-            perror("fcntl");
-            close(mfd);
-            return NULL;
-        }
-    } else {
+    if (mfd == -1) {
         const char *tmpdir = g_get_tmp_dir();
         gchar *fname;
 
-- 
2.15.0.rc0.40.gaefcc5f6f