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memory: add readonly support to memory_region_init_ram_from_file()

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There is currently no way to open(O_RDONLY) and mmap(PROT_READ) when
creating a memory region from a file. This functionality is needed since
the underlying host file may not allow writing.

Add a bool readonly argument to memory_region_init_ram_from_file() and
the APIs it calls.

Extend memory_region_init_ram_from_file() rather than introducing a
memory_region_init_rom_from_file() API so that callers can easily make a
choice between read/write and read-only at runtime without calling
different APIs.

No new RAMBlock flag is introduced for read-only because it's unclear
whether RAMBlocks need to know that they are read-only. Pass a bool
readonly argument instead.

Both of these design decisions can be changed in the future. It just
seemed like the simplest approach to me.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20210104171320.575838-2-stefanha@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2021-01-04 17:13:18 +00:00 • committed by Eduardo Habkost
parent 74208cd252
commit 369d6dc4de
8 changed files with 31 additions and 17 deletions
Download patch file Download diff file Expand all files Collapse all files

10
util/mmap-alloc.c
View file

@ -85,9 +85,11 @@ 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)
{
int prot;
int flags;
int map_sync_flags = 0;
int guardfd;
@ -146,8 +148,9 @@ 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);
prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
ptr = mmap(guardptr + offset, size, prot, flags | map_sync_flags, fd, 0);
if (ptr == MAP_FAILED && map_sync_flags) {
if (errno == ENOTSUP) {
@ -171,8 +174,7 @@ void *qemu_ram_mmap(int fd,
* if map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
* we will remove these flags to handle compatibility.
*/
ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
flags, fd, 0);
ptr = mmap(guardptr + offset, size, prot, flags, fd, 0);
}
if (ptr == MAP_FAILED) {

2
util/oslib-posix.c
View file

@ -230,7 +230,7 @@ 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, false, shared, false);
if (ptr == MAP_FAILED) {
return NULL;