[Qemu-devel] [PATCH v2 3/9] osdep: add memfd helpers

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

Add qemu_memfd_alloc/free() helpers.

The function helps to allocate and seal a memfd, and implements an
open/unlink/mmap fallback for system that do not support memfd.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 include/qemu/memfd.h |  4 +++
 util/memfd.c         | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
index 8b1fe6a..950fb88 100644
--- a/include/qemu/memfd.h
+++ b/include/qemu/memfd.h
@@ -17,4 +17,8 @@
 #define F_SEAL_WRITE    0x0008  /* prevent writes */
 #endif
 
+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);
+
 #endif /* QEMU_MEMFD_H */
diff --git a/util/memfd.c b/util/memfd.c
index a98d57e..8b2b785 100644
--- a/util/memfd.c
+++ b/util/memfd.c
@@ -27,6 +27,14 @@
 
 #include "config-host.h"
 
+#include <glib.h>
+#include <glib/gprintf.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+
 #include "qemu/memfd.h"
 
 #ifdef CONFIG_MEMFD
@@ -44,13 +52,75 @@
 #define MFD_ALLOW_SEALING 0x0002U
 #endif
 
-static inline int memfd_create(const char *name, unsigned int flags)
+static int memfd_create(const char *name, unsigned int flags)
 {
     return syscall(__NR_memfd_create, name, flags);
 }
 #else /* !LINUX */
-static inline int memfd_create(const char *name, unsigned int flags)
+static int memfd_create(const char *name, unsigned int flags)
 {
     return -1;
 }
 #endif
+
+void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
+                       int *fd)
+{
+    void *ptr;
+    int mfd;
+
+    mfd = memfd_create(name, MFD_ALLOW_SEALING|MFD_CLOEXEC);
+    if (mfd != -1) {
+        if (ftruncate(mfd, size) == -1) {
+            perror("ftruncate");
+            close(mfd);
+            return NULL;
+        }
+
+        if (fcntl(mfd, F_ADD_SEALS, seals) == -1) {
+            perror("fcntl");
+            close(mfd);
+            return NULL;
+        }
+    } else {
+        const char *tmpdir = getenv("TMPDIR");
+        gchar *fname;
+
+        tmpdir = tmpdir ? tmpdir : "/tmp";
+
+        fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir);
+        mfd = mkstemp(fname);
+        unlink(fname);
+        g_free(fname);
+
+        if (mfd == -1) {
+            perror("mkstemp");
+            return NULL;
+        }
+
+        if (ftruncate(mfd, size) == -1) {
+            perror("ftruncate");
+            close(mfd);
+            return NULL;
+        }
+    }
+
+    ptr = mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, mfd, 0);
+    if (ptr == MAP_FAILED) {
+        perror("mmap");
+        close(mfd);
+        return NULL;
+    }
+
+    *fd = mfd;
+    return ptr;
+}
+
+void qemu_memfd_free(void *ptr, size_t size, int fd)
+{
+    if (ptr) {
+        munmap(ptr, size);
+    }
+
+    close(fd);
+}
-- 
2.4.3