Re: [PATCH v12 03/19] memory: alloc RAM from file at offset

["Marc-André Lureau" <marcandre.lureau@gmail.com>]

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On Wed, Dec 2, 2020 at 12:23 AM Jagannathan Raman <jag.raman@oracle.com>
wrote:

> Allow RAM MemoryRegion to be created from an offset in a file, instead
> of allocating at offset of 0 by default. This is needed to synchronize
> RAM between QEMU & remote process.
>
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  include/exec/memory.h     |  2 ++
>  include/exec/ram_addr.h   |  2 +-
>  include/qemu/mmap-alloc.h |  3 ++-
>  backends/hostmem-memfd.c  |  2 +-
>  hw/misc/ivshmem.c         |  3 ++-
>  softmmu/memory.c          |  3 ++-
>  softmmu/physmem.c         | 11 +++++++----
>  util/mmap-alloc.c         |  7 ++++---
>  util/oslib-posix.c        |  2 +-
>  9 files changed, 22 insertions(+), 13 deletions(-)
>
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 0f3e6bc..7bcaada 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -980,6 +980,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
>   * @size: size of the region.
>   * @share: %true if memory must be mmaped with the MAP_SHARED flag
>   * @fd: the fd to mmap.
> + * @offset: offset within the file referenced by fd
>   * @errp: pointer to Error*, to store an error if it happens.
>   *
>   * Note that this function does not do anything to cause the data in the
> @@ -991,6 +992,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
>                                      uint64_t size,
>                                      bool share,
>                                      int fd,
> +                                    ram_addr_t offset,
>                                      Error **errp);
>  #endif
>
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index c6d2ef1..d465a48 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -121,7 +121,7 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size,
> MemoryRegion *mr,
>                                     Error **errp);
>  RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
>                                   uint32_t ram_flags, int fd,
> -                                 Error **errp);
> +                                 off_t offset, Error **errp);
>
>  RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>                                    MemoryRegion *mr, Error **errp);
> diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> index e786266..4f57985 100644
> --- a/include/qemu/mmap-alloc.h
> +++ b/include/qemu/mmap-alloc.h
> @@ -25,7 +25,8 @@ void *qemu_ram_mmap(int fd,
>                      size_t size,
>                      size_t align,
>                      bool shared,
> -                    bool is_pmem);
> +                    bool is_pmem,
> +                    off_t start);
>

I'd suggest to keep the variable name  "offset", to avoid potential
confusion (it's also the name of the mmap() argument).


>  void qemu_ram_munmap(int fd, void *ptr, size_t size);
>
> diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
> index e5626d4..69b0ae3 100644
> --- a/backends/hostmem-memfd.c
> +++ b/backends/hostmem-memfd.c
> @@ -55,7 +55,7 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend,
> Error **errp)
>      name = host_memory_backend_get_name(backend);
>      memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend),
>                                     name, backend->size,
> -                                   backend->share, fd, errp);
> +                                   backend->share, fd, 0, errp);
>      g_free(name);
>  }
>
> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> index e321e5c..8d3e1ee 100644
> --- a/hw/misc/ivshmem.c
> +++ b/hw/misc/ivshmem.c
> @@ -494,7 +494,8 @@ static void process_msg_shmem(IVShmemState *s, int fd,
> Error **errp)
>
>      /* mmap the region and map into the BAR2 */
>      memory_region_init_ram_from_fd(&s->server_bar2, OBJECT(s),
> -                                   "ivshmem.bar2", size, true, fd,
> &local_err);
> +                                   "ivshmem.bar2", size, true, fd, 0,
> +                                   &local_err);
>      if (local_err) {
>          error_propagate(errp, local_err);
>          return;
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index 11ca94d..e4ed0e4 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -1612,6 +1612,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
>                                      uint64_t size,
>                                      bool share,
>                                      int fd,
> +                                    ram_addr_t offset,
>                                      Error **errp)
>  {
>      Error *err = NULL;
> @@ -1621,7 +1622,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
>      mr->destructor = memory_region_destructor_ram;
>      mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
>                                             share ? RAM_SHARED : 0,
> -                                           fd, &err);
> +                                           fd, offset, &err);
>      mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
>      if (err) {
>          mr->size = int128_zero();
> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
> index 3027747..e0b8fc6 100644
> --- a/softmmu/physmem.c
> +++ b/softmmu/physmem.c
> @@ -1461,6 +1461,7 @@ static void *file_ram_alloc(RAMBlock *block,
>                              ram_addr_t memory,
>                              int fd,
>                              bool truncate,
> +                            off_t offset,
>                              Error **errp)
>  {
>      void *area;
> @@ -1511,7 +1512,8 @@ static void *file_ram_alloc(RAMBlock *block,
>      }
>
>      area = qemu_ram_mmap(fd, memory, block->mr->align,
> -                         block->flags & RAM_SHARED, block->flags &
> RAM_PMEM);
> +                         block->flags & RAM_SHARED, block->flags &
> RAM_PMEM,
> +                         offset);
>      if (area == MAP_FAILED) {
>          error_setg_errno(errp, errno,
>                           "unable to map backing store for guest RAM");
> @@ -1943,7 +1945,7 @@ static void ram_block_add(RAMBlock *new_block, Error
> **errp, bool shared)
>  #ifdef CONFIG_POSIX
>  RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
>                                   uint32_t ram_flags, int fd,
> -                                 Error **errp)
> +                                 off_t offset, Error **errp)
>  {
>      RAMBlock *new_block;
>      Error *local_err = NULL;
> @@ -1996,7 +1998,8 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size,
> MemoryRegion *mr,
>      new_block->used_length = size;
>      new_block->max_length = size;
>      new_block->flags = ram_flags;
> -    new_block->host = file_ram_alloc(new_block, size, fd, !file_size,
> errp);
> +    new_block->host = file_ram_alloc(new_block, size, fd, !file_size,
> offset,
> +                                     errp);
>      if (!new_block->host) {
>          g_free(new_block);
>          return NULL;
> @@ -2026,7 +2029,7 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size,
> MemoryRegion *mr,
>          return NULL;
>      }
>
> -    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, errp);
> +    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, 0, errp);
>      if (!block) {
>          if (created) {
>              unlink(mem_path);
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 27dcccd..a28f702 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -86,7 +86,8 @@ void *qemu_ram_mmap(int fd,
>                      size_t size,
>                      size_t align,
>                      bool shared,
> -                    bool is_pmem)
> +                    bool is_pmem,
> +                    off_t start)
>  {
>      int flags;
>      int map_sync_flags = 0;
> @@ -147,7 +148,7 @@ void *qemu_ram_mmap(int fd,
>      offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) -
> (uintptr_t)guardptr;
>
>      ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
> -               flags | map_sync_flags, fd, 0);
> +               flags | map_sync_flags, fd, start);
>
>      if (ptr == MAP_FAILED && map_sync_flags) {
>          if (errno == ENOTSUP) {
> @@ -172,7 +173,7 @@ void *qemu_ram_mmap(int fd,
>           * we will remove these flags to handle compatibility.
>           */
>          ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
> -                   flags, fd, 0);
> +                   flags, fd, start);
>      }
>
>      if (ptr == MAP_FAILED) {
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index f15234b..93874df 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -227,7 +227,7 @@ void *qemu_memalign(size_t alignment, size_t size)
>  void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared)
>  {
>      size_t align = QEMU_VMALLOC_ALIGN;
> -    void *ptr = qemu_ram_mmap(-1, size, align, shared, false);
> +    void *ptr = qemu_ram_mmap(-1, size, align, shared, false, 0);
>
>      if (ptr == MAP_FAILED) {
>          return NULL;
> --
> 1.8.3.1
>
>

-- 
Marc-André Lureau

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