Currently, if a file does not exist yet, file_ram_open() will create new
empty file and open it writable. However, it even does that when
readonly=true was specified.
Specifying O_RDONLY instead to create a new readonly file would
theoretically work, however, ftruncate() will refuse to resize the new
empty file and we'll get a warning:
ftruncate: Invalid argument
And later eventually more problems when actually mmap'ing that file and
accessing it.
If someone intends to let QEMU open+mmap a file read-only, better
create+resize+fill that file ahead of time outside of QEMU context.
We'll now fail with:
./qemu-system-x86_64 \
-object memory-backend-file,id=ram0,mem-path=tmp,readonly=true,size=1g
qemu-system-x86_64: can't open backing store tmp for guest RAM: No such file or directory
All use cases of readonly files (R/O NVDIMMs, VM templating) work on
existing files, so silently creating new files might just hide user
errors when accidentally specifying a non-existent file.
Note that the only memory-backend-file will end up calling
memory_region_init_ram_from_file() -> qemu_ram_alloc_from_file() ->
file_ram_open().
Move error reporting to the single caller.
Signed-off-by: David Hildenbrand <david@redhat.com>
---
softmmu/physmem.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 32d641754b..f8c47ecb85 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -1289,8 +1289,7 @@ 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)
+ bool *created)
{
char *filename;
char *sanitized_name;
@@ -1305,6 +1304,10 @@ static int file_ram_open(const char *path,
break;
}
if (errno == ENOENT) {
+ if (readonly) {
+ /* Refuse to create new, readonly files. */
+ return -ENOENT;
+ }
/* @path names a file that doesn't exist, create it */
fd = open(path, O_RDWR | O_CREAT | O_EXCL, 0644);
if (fd >= 0) {
@@ -1334,10 +1337,7 @@ static int file_ram_open(const char *path,
g_free(filename);
}
if (errno != EEXIST && errno != EINTR) {
- error_setg_errno(errp, errno,
- "can't open backing store %s for guest RAM",
- path);
- return -1;
+ return -errno;
}
/*
* Try again on EINTR and EEXIST. The latter happens when
@@ -1947,8 +1947,10 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
RAMBlock *block;
fd = file_ram_open(mem_path, memory_region_name(mr),
- !!(ram_flags & RAM_READONLY_FD), &created, errp);
+ !!(ram_flags & RAM_READONLY_FD), &created);
if (fd < 0) {
+ error_setg_errno(errp, -fd, "can't open backing store %s for guest RAM",
+ mem_path);
return NULL;
}
--
2.41.0