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>

3 files changed, 7 insertions, 2 deletions

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 521d9901d7..c6ce74fb79 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -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);
 
 /**
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index c6d2ef1d07..40b16609ab 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);