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[Qemu-devel] [PATCH v2 1/2] util/mmap-alloc: support MAP_SYNC in qemu_ra
From: |
Haozhong Zhang |
Subject: |
[Qemu-devel] [PATCH v2 1/2] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap() |
Date: |
Thu, 11 Jan 2018 22:22:07 +0800 |
When a file supporting DAX is used as vNVDIMM backend, mmap it with
MAP_SYNC flag in addition can guarantee the persistence of guest write
to the backend file without other QEMU actions (e.g., periodic fsync()
by QEMU).
A OnOffAuto parameter 'sync' is added to qemu_ram_mmap():
- If sync == ON_OFF_AUTO_ON, qemu_ram_mmap() will try to pass MAP_SYNC
to mmap(). It will then fail if the host OS or the backend file do
not support MAP_SYNC, or MAP_SYNC is conflict with other flags.
- If sync == ON_OFF_AUTO_OFF, qemu_ram_mmap() will never pass MAP_SYNC
to mmap().
- If sync == ON_OFF_AUTO_AUTO, and
* if the host OS and the backend file support MAP_SYNC, and MAP_SYNC
is not conflict with other flags, qemu_ram_mmap() will work as if
sync == ON_OFF_AUTO_ON.
* otherwise, qemu_ram_mmap() will work as if sync == ON_OFF_AUTO_OFF.
Signed-off-by: Haozhong Zhang <address@hidden>
---
exec.c | 2 +-
include/qemu/mmap-alloc.h | 3 ++-
include/qemu/osdep.h | 16 ++++++++++++++++
util/mmap-alloc.c | 24 ++++++++++++++++++++++--
util/oslib-posix.c | 2 +-
5 files changed, 42 insertions(+), 5 deletions(-)
diff --git a/exec.c b/exec.c
index 8fba88ae1c..f4254cb6d3 100644
--- a/exec.c
+++ b/exec.c
@@ -1646,7 +1646,7 @@ static void *file_ram_alloc(RAMBlock *block,
}
area = qemu_ram_mmap(fd, memory, block->mr->align,
- block->flags & RAM_SHARED);
+ block->flags & RAM_SHARED, ON_OFF_AUTO_OFF);
if (area == MAP_FAILED) {
error_setg_errno(errp, errno,
"unable to map backing store for guest RAM");
diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
index 50385e3f81..dd5876471f 100644
--- a/include/qemu/mmap-alloc.h
+++ b/include/qemu/mmap-alloc.h
@@ -7,7 +7,8 @@ size_t qemu_fd_getpagesize(int fd);
size_t qemu_mempath_getpagesize(const char *mem_path);
-void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared);
+void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared,
+ OnOffAuto sync);
void qemu_ram_munmap(void *ptr, size_t size);
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index adb3758275..55637e0724 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -372,6 +372,22 @@ void qemu_anon_ram_free(void *ptr, size_t size);
# define QEMU_VMALLOC_ALIGN getpagesize()
#endif
+/*
+ * MAP_SHARED_VALIDATE and MAP_SYNC were introduced in Linux kernel
+ * 4.15, so they may not be defined when compiling on older kernels.
+ */
+#ifdef CONFIG_LINUX
+#ifndef MAP_SHARED_VALIDATE
+#define MAP_SHARED_VALIDATE 0x3
+#endif
+#ifndef MAP_SYNC
+#define MAP_SYNC 0x80000
+#endif
+#define QEMU_HAS_MAP_SYNC true
+#else /* !CONFIG_LINUX */
+#define QEMU_HAS_MAP_SYNC false
+#endif /* CONFIG_LINUX */
+
#ifdef CONFIG_POSIX
struct qemu_signalfd_siginfo {
uint32_t ssi_signo; /* Signal number */
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 2fd8cbcc6f..af57218669 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -73,7 +73,8 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
return getpagesize();
}
-void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
+void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared,
+ OnOffAuto sync)
{
/*
* Note: this always allocates at least one extra page of virtual address
@@ -97,6 +98,7 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, bool
shared)
#endif
size_t offset;
void *ptr1;
+ int xflags = 0;
if (ptr == MAP_FAILED) {
return MAP_FAILED;
@@ -106,11 +108,29 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align,
bool shared)
/* Always align to host page size */
assert(align >= getpagesize());
+ if (!QEMU_HAS_MAP_SYNC || !shared) {
+ if (sync == ON_OFF_AUTO_ON) {
+ return MAP_FAILED;
+ }
+ sync = ON_OFF_AUTO_OFF;
+ }
+ if (sync != ON_OFF_AUTO_OFF) {
+ xflags = MAP_SYNC;
+ }
+ /*
+ * If MAP_SHARED_VALIDATE is present, mmap will fail when MAP_SYNC
+ * is not supported. Otherwise, mmap will just ignore MAP_SYNC when
+ * it's not supported.
+ */
+ if (sync == ON_OFF_AUTO_ON) {
+ xflags |= MAP_SHARED_VALIDATE;
+ }
+
offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
MAP_FIXED |
(fd == -1 ? MAP_ANONYMOUS : 0) |
- (shared ? MAP_SHARED : MAP_PRIVATE),
+ (shared ? MAP_SHARED : MAP_PRIVATE) | xflags,
fd, 0);
if (ptr1 == MAP_FAILED) {
munmap(ptr, total);
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 77369c92ce..ecb1c275d2 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -130,7 +130,7 @@ void *qemu_memalign(size_t alignment, size_t size)
void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment)
{
size_t align = QEMU_VMALLOC_ALIGN;
- void *ptr = qemu_ram_mmap(-1, size, align, false);
+ void *ptr = qemu_ram_mmap(-1, size, align, false, ON_OFF_AUTO_OFF);
if (ptr == MAP_FAILED) {
return NULL;
--
2.15.1