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[PATCH v2 1/3] memory: add readonly support to memory_region_init_ram_fr
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From: |
Stefan Hajnoczi |
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Subject: |
[PATCH v2 1/3] memory: add readonly support to memory_region_init_ram_from_file() |
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Date: |
Wed, 16 Sep 2020 10:51:48 +0100 |
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.
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
include/exec/memory.h | 2 ++
include/exec/ram_addr.h | 5 +++--
include/qemu/mmap-alloc.h | 2 ++
backends/hostmem-file.c | 2 +-
exec.c | 18 +++++++++++-------
softmmu/memory.c | 7 +++++--
util/mmap-alloc.c | 10 ++++++----
util/oslib-posix.c | 2 +-
8 files changed, 31 insertions(+), 17 deletions(-)
diff --git a/include/exec/memory.h b/include/exec/memory.h
index f1bb2a7df5..a81fa26165 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -879,6 +879,7 @@ 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
@@ -891,6 +892,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t align,
uint32_t ram_flags,
const char *path,
+ bool readonly,
Error **errp);
/**
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 3ef729a23c..2a0360a0f2 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -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,
diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
index e786266b92..8b7a5c70f3 100644
--- a/include/qemu/mmap-alloc.h
+++ b/include/qemu/mmap-alloc.h
@@ -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);
diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index a3b2e8209e..dffdf142e0 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -58,7 +58,7 @@ 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
}
diff --git a/exec.c b/exec.c
index e34b602bdf..f1e82dad7a 100644
--- a/exec.c
+++ b/exec.c
@@ -1770,6 +1770,7 @@ 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)
{
@@ -1780,7 +1781,7 @@ 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;
@@ -1832,6 +1833,7 @@ 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)
{
@@ -1882,7 +1884,7 @@ 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,
@@ -2314,7 +2316,7 @@ 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;
@@ -2368,7 +2370,8 @@ 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;
@@ -2387,18 +2390,19 @@ 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);
diff --git a/softmmu/memory.c b/softmmu/memory.c
index d030eb6f7c..1b0d1d42c6 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1553,15 +1553,18 @@ 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);
mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
if (err) {
mr->size = int128_zero();
@@ -1585,7 +1588,7 @@ 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);
mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
if (err) {
mr->size = int128_zero();
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 27dcccd8ec..890fda6a35 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -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) {
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index ad8001a4ad..236b3a88c1 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -227,7 +227,7 @@ 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;
--
2.26.2