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Re: [PATCH v4 09/14] util/mmap-alloc: Pass flags instead of separate boo


From: David Hildenbrand
Subject: Re: [PATCH v4 09/14] util/mmap-alloc: Pass flags instead of separate bools to qemu_ram_mmap()
Date: Thu, 25 Mar 2021 10:40:03 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0

On 23.03.21 21:49, Peter Xu wrote:
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


Nice catch, thanks :)


--
Thanks,

David / dhildenb




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