Re: [PATCH v4 09/14] util/mmap-alloc: Pass flags instead of separate bools to qemu_ram_mmap()

[Peter Xu]

On Fri, Mar 19, 2021 at 11:12:25AM +0100, David Hildenbrand wrote:
> Let's pass flags instead of bools to prepare for passing other flags and
> update the documentation of qemu_ram_mmap(). Introduce new QEMU_MAP_
> flags that abstract the mmap() PROT_ and MAP_ flag handling and simplify
> it.
> 
> We expose only flags that are currently supported by qemu_ram_mmap().
> Maybe, we'll see qemu_mmap() in the future as well that can implement these
> flags.
> 
> Note: We don't use MAP_ flags as some flags (e.g., MAP_SYNC) are only
> defined for some systems and we want to always be able to identify
> these flags reliably inside qemu_ram_mmap() -- for example, to properly
> warn when some future flags are not available or effective on a system.
> Also, this way we can simplify PROT_ handling as well.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  include/qemu/mmap-alloc.h | 16 +++++++++-------
>  include/qemu/osdep.h      | 18 ++++++++++++++++++
>  softmmu/physmem.c         |  8 +++++---
>  util/mmap-alloc.c         | 15 ++++++++-------
>  util/oslib-posix.c        |  3 ++-
>  5 files changed, 42 insertions(+), 18 deletions(-)
> 
> diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> index 456ff87df1..a60a2085b3 100644
> --- a/include/qemu/mmap-alloc.h
> +++ b/include/qemu/mmap-alloc.h
> @@ -7,18 +7,22 @@ size_t qemu_fd_getpagesize(int fd);
>  size_t qemu_mempath_getpagesize(const char *mem_path);
>  
>  /**
> - * qemu_ram_mmap: mmap the specified file or device.
> + * qemu_ram_mmap: mmap anonymous memory, the specified file or device.
> + *
> + * mmap() abstraction to map guest RAM, simplifying flag handling, taking
> + * care of alignment requirements and installing guard pages.
>   *
>   * 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.
> - *  @readonly: true for a read-only mapping, false for read/write.
> - *  @shared: map has RAM_SHARED flag.
> - *  @is_pmem: map has RAM_PMEM flag.
> + *  @qemu_map_flags: QEMU_MAP_* flags
>   *  @map_offset: map starts at offset of map_offset from the start of fd
>   *
> + * Internally, MAP PRIVATE, MAP_ANONYMOUS and MAP_SHARED_VALIDATE are set
                     ^
                     |
                     +---- underscore

> + * implicitly based on other parameters.
> + *

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu