On Wed, Jan 23, 2019 at 10:59:45AM +0800, Zhang, Yi wrote:
> From: Zhang Yi <yi.z.zh...@linux.intel.com>
>
> When a file supporting DAX is used as vNVDIMM backend, mmap it with
> MAP_SYNC flag in addition which can ensure file system metadata
> synced in each guest writes to the backend file, without other QEMU
> actions (e.g., periodic fsync() by QEMU).
>
> Current, We have below different possible use cases:
>
> 1. pmem=on is set, shared=on is set, MAP_SYNC supported:
> a: backend is a dax supporting file.
> - MAP_SYNC will active.
> b: backend is not a dax supporting file.
> - mmap will result in an EOPNOTSUPP error.
>
> 2. The rest of cases:
> - we will never pass the MAP_SYNC to mmap2
>
> Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com>
> Signed-off-by: Zhang Yi <yi.z.zh...@linux.intel.com>
> ---
> include/qemu/mmap-alloc.h | 1 +
> include/qemu/osdep.h | 21 +++++++++++++++++++++
> util/mmap-alloc.c | 7 ++++++-
> 3 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> index 6fe6ed4..a95d91c 100644
> --- a/include/qemu/mmap-alloc.h
> +++ b/include/qemu/mmap-alloc.h
> @@ -18,6 +18,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
> * @flags: specifies additional properties of the mapping, which can be one
> or
> * bit-or of following values
> * - RAM_SHARED: mmap with MAP_SHARED flag
> + * - RAM_PMEM: mmap with MAP_SYNC flag
> * Other bits are ignored.
> *
> * Return:
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 457d24e..3bcf155 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -419,6 +419,27 @@ void qemu_anon_ram_free(void *ptr, size_t size);
> # define QEMU_VMALLOC_ALIGN getpagesize()
> #endif
>
> +/*
> + * MAP_SHARED_VALIDATE and MAP_SYNC are introduced in Linux kernel
> + * 4.15, so they may not be defined when compiling on older kernels.
> + */
I commented on this part in v7. That's a wrong way to handle
compatibility.
> +#ifdef CONFIG_LINUX
> +
> +#include <linux/mman.h>
> +
> +#ifndef MAP_SYNC
> +#define MAP_SYNC 0x0
> +#endif
> +
> +#ifndef MAP_SHARED_VALIDATE
> +#define MAP_SHARED_VALIDATE 0x0
> +#endif
> +
> +#else /* !CONFIG_LINUX */
> +#define MAP_SYNC 0x0
> +#define MAP_SHARED_VALIDATE 0x0
> +#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 8f0a740..a4ce9b5 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -99,6 +99,8 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align,
> uint32_t flags)
> void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1,
> 0);
> #endif
> bool shared = flags & RAM_SHARED;
> + bool is_pmem = flags & RAM_PMEM;
> + int mmap_xflags = 0;
> size_t offset;
> void *ptr1;
>
> @@ -109,12 +111,15 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align,
> uint32_t flags)
> assert(is_power_of_2(align));
> /* Always align to host page size */
> assert(align >= getpagesize());
> + if (shared && is_pmem) {
> + mmap_xflags |= (MAP_SYNC | 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) | mmap_xflags,
> fd, 0);
> if (ptr1 == MAP_FAILED) {
> munmap(ptr, total);
> --
> 2.7.4
