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util/mmap-alloc: Pass flags instead of separate bools to qemu_ram_mmap()

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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.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Eduardo Habkost <ehabkost@redhat.com> for memory backend and machine core
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210510114328.21835-8-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Hildenbrand 2021-05-10 13:43:20 +02:00 • committed by Paolo Bonzini
parent ebef62d0e5
commit b444f5c079
5 changed files with 42 additions and 18 deletions
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16
include/qemu/mmap-alloc.h
View file

@ -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
* implicitly based on other parameters.
*
* Return:
* On success, return a pointer to the mapped area.
* On failure, return MAP_FAILED.
@ -26,9 +30,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
void *qemu_ram_mmap(int fd,
size_t size,
size_t align,
bool readonly,
bool shared,
bool is_pmem,
uint32_t qemu_map_flags,
off_t map_offset);
void qemu_ram_munmap(int fd, void *ptr, size_t size);

18
include/qemu/osdep.h
View file

@ -366,6 +366,24 @@ void *qemu_anon_ram_alloc(size_t size, uint64_t *align, bool shared);
void qemu_vfree(void *ptr);
void qemu_anon_ram_free(void *ptr, size_t size);
/*
* Abstraction of PROT_ and MAP_ flags as passed to mmap(), for example,
* consumed by qemu_ram_mmap().
*/
/* Map PROT_READ instead of PROT_READ | PROT_WRITE. */
#define QEMU_MAP_READONLY (1 << 0)
/* Use MAP_SHARED instead of MAP_PRIVATE. */
#define QEMU_MAP_SHARED (1 << 1)
/*
* Use MAP_SYNC | MAP_SHARED_VALIDATE if supported. Ignored without
* QEMU_MAP_SHARED. If mapping fails, warn and fallback to !QEMU_MAP_SYNC.
*/
#define QEMU_MAP_SYNC (1 << 2)
#define QEMU_MADV_INVALID -1
#if defined(CONFIG_MADVISE)