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).
Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com> Signed-off-by: Zhang Yi <yi.z.zh...@linux.intel.com> --- include/qemu/osdep.h | 16 ++++++++++++++++ util/mmap-alloc.c | 12 +++++++++++- 2 files changed, 27 insertions(+), 1 deletion(-) diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index 3bf48bc..bb1eba1 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -410,6 +410,22 @@ 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. + */ +#ifdef CONFIG_LINUX + +#include <asm-generic/mman.h> + +#ifndef MAP_SYNC +#define MAP_SYNC 0x0 +#endif + +#else /* !CONFIG_LINUX */ +#define MAP_SYNC 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..a9d5e56 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; @@ -109,13 +111,21 @@ 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; + } offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr; + retry_mmap_fd: 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) && (mmap_xflags & MAP_SYNC)) { + mmap_xflags &= ~MAP_SYNC; + goto retry_mmap_fd; + } if (ptr1 == MAP_FAILED) { munmap(ptr, total); return MAP_FAILED; -- 2.7.4