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memory: add readonly support to memory_region_init_ram_from_file() 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
backends/hostmem-file.c
View File

@ -56,7 +56,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
backend->size, fb->align,
(backend->share ? RAM_SHARED : 0) |
(fb->is_pmem ? RAM_PMEM : 0),
fb->mem_path, errp);
fb->mem_path, false, errp);
g_free(name);
#endif
}

2
include/exec/memory.h
View File

@ -966,6 +966,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
* - RAM_PMEM: the memory is persistent memory
* Other bits are ignored now.
* @path: the path in which to allocate the RAM.
* @readonly: true to open @path for reading, false for read/write.
* @errp: pointer to Error*, to store an error if it happens.
*
* Note that this function does not do anything to cause the data in the
@ -978,6 +979,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t align,
uint32_t ram_flags,
const char *path,
bool readonly,
Error **errp);
/**

5
include/exec/ram_addr.h
View File

@ -110,6 +110,7 @@ long qemu_maxrampagesize(void);
* - RAM_PMEM: the backend @mem_path or @fd is persistent memory
* Other bits are ignored.
* @mem_path or @fd: specify the backing file or device
* @readonly: true to open @path for reading, false for read/write.
* @errp: pointer to Error*, to store an error if it happens
*
* Return:
@ -118,9 +119,9 @@ long qemu_maxrampagesize(void);
*/
RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, const char *mem_path,
Error **errp);
bool readonly, Error **errp);
RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, int fd,
uint32_t ram_flags, int fd, bool readonly,
Error **errp);
RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,

2
include/qemu/mmap-alloc.h
View File

@ -14,6 +14,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
* @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.
*
@ -24,6 +25,7 @@ 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);

7
softmmu/memory.c
View File

@ -1587,15 +1587,18 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t align,
uint32_t ram_flags,
const char *path,
bool readonly,
Error **errp)
{
Error *err = NULL;
memory_region_init(mr, owner, name, size);
mr->ram = true;
mr->readonly = readonly;
mr->terminates = true;
mr->destructor = memory_region_destructor_ram;
mr->align = align;
mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, &err);
mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path,
readonly, &err);
if (err) {
mr->size = int128_zero();
object_unparent(OBJECT(mr));
@ -1618,7 +1621,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
mr->destructor = memory_region_destructor_ram;
mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
share ? RAM_SHARED : 0,
fd, &err);
fd, false, &err);
if (err) {
mr->size = int128_zero();
object_unparent(OBJECT(mr));

18
softmmu/physmem.c
View File

@ -1398,6 +1398,7 @@ static int64_t get_file_align(int fd)
static int file_ram_open(const char *path,
const char *region_name,
bool readonly,
bool *created,
Error **errp)
{
@ -1408,7 +1409,7 @@ static int file_ram_open(const char *path,
*created = false;
for (;;) {
fd = open(path, O_RDWR);
fd = open(path, readonly ? O_RDONLY : O_RDWR);
if (fd >= 0) {
/* @path names an existing file, use it */
break;
@ -1460,6 +1461,7 @@ static int file_ram_open(const char *path,
static void *file_ram_alloc(RAMBlock *block,
ram_addr_t memory,
int fd,
bool readonly,
bool truncate,
Error **errp)
{
@ -1510,7 +1512,7 @@ static void *file_ram_alloc(RAMBlock *block,
perror("ftruncate");
}
area = qemu_ram_mmap(fd, memory, block->mr->align,
area = qemu_ram_mmap(fd, memory, block->mr->align, readonly,
block->flags & RAM_SHARED, block->flags & RAM_PMEM);
if (area == MAP_FAILED) {
error_setg_errno(errp, errno,
@ -1942,7 +1944,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp, bool shared)
#ifdef CONFIG_POSIX
RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, int fd,
uint32_t ram_flags, int fd, bool readonly,
Error **errp)
{
RAMBlock *new_block;
@ -1996,7 +1998,8 @@ 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, readonly,
!file_size, errp);
if (!new_block->host) {
g_free(new_block);
return NULL;
@ -2015,18 +2018,19 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, const char *mem_path,
Error **errp)
bool readonly, Error **errp)
{
int fd;
bool created;
RAMBlock *block;
fd = file_ram_open(mem_path, memory_region_name(mr), &created, errp);
fd = file_ram_open(mem_path, memory_region_name(mr), readonly, &created,
errp);
if (fd < 0) {
return NULL;
}
block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, errp);
block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, readonly, errp);
if (!block) {
if (created) {
unlink(mem_path);

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;