Re: [Qemu-devel] [PATCH V8 2/5] util/mmap-alloc: switch qemu_ram_mmap() to 'flags' parameter

[Eduardo Habkost]

On Wed, Jan 02, 2019 at 01:26:06PM +0800, Zhang Yi wrote:
> As more flag parameters besides the existing 'shared' are going to be
> added to qemu_ram_mmap(), let's switch 'shared' to a 'flags' parameter
> in advance, so as to ease the further additions.
> 
> Signed-off-by: Haozhong Zhang <address@hidden>
> Signed-off-by: Zhang Yi <address@hidden>
> ---
>  exec.c                    |  7 ++++---
>  include/exec/memory.h     | 22 ++++++++++++++++------
>  include/qemu/mmap-alloc.h | 19 ++++++++++++++++++-
>  util/mmap-alloc.c         |  8 +++++---
>  util/oslib-posix.c        |  9 ++++++++-
>  5 files changed, 51 insertions(+), 14 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index bb6170d..e92a7da 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1810,6 +1810,7 @@ static void *file_ram_alloc(RAMBlock *block,
>                              ram_addr_t memory,
>                              int fd,
>                              bool truncate,
> +                            uint32_t flags,
>                              Error **errp)

I suggest documenting on the commit message why you are changing
file_ram_alloc() too.  The commit message mentions only
qemu_ram_mmap().

>  {
>      void *area;
> @@ -1859,8 +1860,7 @@ static void *file_ram_alloc(RAMBlock *block,
>          perror("ftruncate");
>      }
>  
> -    area = qemu_ram_mmap(fd, memory, block->mr->align,
> -                         block->flags & RAM_SHARED);
> +    area = qemu_ram_mmap(fd, memory, block->mr->align, flags);
>      if (area == MAP_FAILED) {
>          error_setg_errno(errp, errno,
>                           "unable to map backing store for guest RAM");
> @@ -2279,7 +2279,8 @@ 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,
> +            ram_flags, errp);
>      if (!new_block->host) {
>          g_free(new_block);
>          return NULL;
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 667466b..6e30c23 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -103,28 +103,38 @@ struct IOMMUNotifier {
>  };
>  typedef struct IOMMUNotifier IOMMUNotifier;
>  
> +#ifdef __CHECKER__
> +#define QEMU_BITWISE __attribute__((bitwise))
> +#define QEMU_FORCE   __attribute__((force))
> +#else
> +#define QEMU_BITWISE
> +#define QEMU_FORCE
> +#endif
> +

I assume this is a sparse feature?

Why is it part of this patch?  I suggest doing this in a separate
patch series and in a common header file, so other developers
have a better chance to review it and decide how to use this
sparse feature in QEMU.


> +typedef unsigned QEMU_BITWISE QemuMmapFlags;
> +
>  /* RAM is pre-allocated and passed into qemu_ram_alloc_from_ptr */
> -#define RAM_PREALLOC   (1 << 0)
> +#define RAM_PREALLOC ((QEMU_FORCE QemuMmapFlags) (1 << 0))
>  
>  /* RAM is mmap-ed with MAP_SHARED */
> -#define RAM_SHARED     (1 << 1)
> +#define RAM_SHARED ((QEMU_FORCE QemuMmapFlags) (1 << 1))
>  
>  /* Only a portion of RAM (used_length) is actually used, and migrated.
>   * This used_length size can change across reboots.
>   */
> -#define RAM_RESIZEABLE (1 << 2)
> +#define RAM_RESIZEABLE ((QEMU_FORCE QemuMmapFlags) (1 << 2))
>  
>  /* UFFDIO_ZEROPAGE is available on this RAMBlock to atomically
>   * zero the page and wake waiting processes.
>   * (Set during postcopy)
>   */
> -#define RAM_UF_ZEROPAGE (1 << 3)
> +#define RAM_UF_ZEROPAGE ((QEMU_FORCE QemuMmapFlags) (1 << 3))
>  
>  /* RAM can be migrated */
> -#define RAM_MIGRATABLE (1 << 4)
> +#define RAM_MIGRATABLE ((QEMU_FORCE QemuMmapFlags) (1 << 4))
>  
>  /* RAM is a persistent kind memory */
> -#define RAM_PMEM (1 << 5)
> +#define RAM_PMEM ((QEMU_FORCE QemuMmapFlags) (1 << 5))
>  
>  static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
>                                         IOMMUNotifierFlag flags,
> diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> index 50385e3..6fe6ed4 100644
> --- a/include/qemu/mmap-alloc.h
> +++ b/include/qemu/mmap-alloc.h
> @@ -7,7 +7,24 @@ 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);
> +/**
> + * qemu_ram_mmap: mmap the specified file or device.
> + *
> + * Parameters:
> + *  @fd: the file or the device to mmap
> + *  @size: the number of bytes to be mmaped
> + *  @align: if not zero, specify the alignment of the starting mapping 
> address;
> + *          otherwise, the alignment in use will be determined by QEMU.
> + *  @flags: specifies additional properties of the mapping, which can be one 
> or
> + *          bit-or of following values
> + *          - RAM_SHARED: mmap with MAP_SHARED flag
> + *          Other bits are ignored.
> + *
> + * Return:
> + *  On success, return a pointer to the mapped area.
> + *  On failure, return MAP_FAILED.
> + */
> +void *qemu_ram_mmap(int fd, size_t size, size_t align, uint32_t flags);
>  
>  void qemu_ram_munmap(void *ptr, size_t size);
>  
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index fd329ec..8f0a740 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -13,6 +13,7 @@
>  #include "qemu/osdep.h"
>  #include "qemu/mmap-alloc.h"
>  #include "qemu/host-utils.h"
> +#include "exec/memory.h"
>  
>  #define HUGETLBFS_MAGIC       0x958458f6
>  
> @@ -75,7 +76,7 @@ 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, uint32_t flags)
>  {
>      /*
>       * Note: this always allocates at least one extra page of virtual address
> @@ -92,11 +93,12 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, 
> bool shared)
>       * anonymous memory is OK.
>       */
>      int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : 
> fd;
> -    int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
> -    void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);
> +    int mmap_flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
> +    void *ptr = mmap(0, total, PROT_NONE, mmap_flags | MAP_PRIVATE, anonfd, 
> 0);
>  #else
>      void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 
> 0);
>  #endif
> +    bool shared = flags & RAM_SHARED;
>      size_t offset;
>      void *ptr1;
>  
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index fbd0dc8..75a0171 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -54,6 +54,7 @@
>  #endif
>  
>  #include "qemu/mmap-alloc.h"
> +#include "exec/memory.h"
>  
>  #ifdef CONFIG_DEBUG_STACK_USAGE
>  #include "qemu/error-report.h"
> @@ -203,7 +204,13 @@ 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);
> +    uint32_t flags = 0;
> +    void *ptr;
> +
> +    if (shared) {
> +        flags = RAM_SHARED;
> +    }
> +    ptr = qemu_ram_mmap(-1, size, align, flags);
>  
>      if (ptr == MAP_FAILED) {
>          return NULL;
> -- 
> 2.7.4
> 
> 

-- 
Eduardo