[Qemu-devel] [PATCH RFC 3/6] osdep: add memfd helpers

[Marc-André Lureau]

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 <address@hidden>
---
 include/qemu/osdep.h |  5 +++++
 util/oslib-posix.c   | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index adc138b..c49145f 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -167,6 +167,11 @@ void *qemu_anon_ram_alloc(size_t size, uint64_t *align);
 void qemu_vfree(void *ptr);
 void qemu_anon_ram_free(void *ptr, size_t size);
 
+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);
+
+
 #define QEMU_MADV_INVALID -1
 
 #if defined(CONFIG_MADVISE)
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 3ae4987..6e5a143 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -482,3 +482,65 @@ int qemu_read_password(char *buf, int buf_size)
     printf("\n");
     return ret;
 }
+
+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