[PATCH kvmtool v1 06/17] Use memfd for hugetlbfs when allocating guest ram

[Fuad Tabba <tabba@google.com>]

This removes the need of using a temporary file for the fd.

Signed-off-by: Fuad Tabba <tabba@google.com>
---
 util/util.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/util/util.c b/util/util.c
index e6c0951..d6ceb5d 100644
--- a/util/util.c
+++ b/util/util.c
@@ -10,6 +10,14 @@
 #include <sys/stat.h>
 #include <sys/statfs.h>
 
+#ifndef MFD_HUGETLB
+#define MFD_HUGETLB	0x0004U
+#endif
+
+#ifndef MFD_HUGE_SHIFT
+#define MFD_HUGE_SHIFT	26
+#endif
+
 static void report(const char *prefix, const char *err, va_list params)
 {
 	char msg[1024];
@@ -96,10 +104,12 @@ static u64 get_hugepage_blk_size(const char *htlbfs_path)
 
 static void *mmap_hugetlbfs(struct kvm *kvm, const char *htlbfs_path, u64 size)
 {
-	char mpath[PATH_MAX];
+	const char *name = "kvmtool";
+	unsigned int flags = 0;
 	int fd;
 	void *addr;
 	u64 blk_size;
+	int htsize;
 
 	blk_size = get_hugepage_blk_size(htlbfs_path);
 	if (blk_size == 0 || blk_size > size) {
@@ -107,13 +117,18 @@ static void *mmap_hugetlbfs(struct kvm *kvm, const char *htlbfs_path, u64 size)
 			(unsigned long long)blk_size, (unsigned long long)size);
 	}
 
+	htsize = __builtin_ctzl(blk_size);
+	if ((1ULL << htsize) != blk_size)
+		die("Hugepage size must be a power of 2.\n");
+
+	flags |= MFD_HUGETLB;
+	flags |= htsize << MFD_HUGE_SHIFT;
+
 	kvm->ram_pagesize = blk_size;
 
-	snprintf(mpath, PATH_MAX, "%s/kvmtoolXXXXXX", htlbfs_path);
-	fd = mkstemp(mpath);
+	fd = memfd_create(name, flags);
 	if (fd < 0)
-		die("Can't open %s for hugetlbfs map\n", mpath);
-	unlink(mpath);
+		die("Can't memfd_create for hugetlbfs map\n");
 	if (ftruncate(fd, size) < 0)
 		die("Can't ftruncate for mem mapping size %lld\n",
 			(unsigned long long)size);
-- 
2.38.1.431.g37b22c650d-goog