softmmu/physmem: Never return directories from file_ram_open()
open() does not fail on directories when opening them readonly (O_RDONLY).
Currently, we succeed opening such directories and fail later during
mmap(), resulting in a misleading error message.
$ ./qemu-system-x86_64 \
-object memory-backend-file,id=ram0,mem-path=tmp,readonly=true,size=1g
qemu-system-x86_64: unable to map backing store for guest RAM: No such device
To identify directories and handle them accordingly in file_ram_open()
also when readonly=true was specified, detect if we just opened a directory
using fstat() instead. Then, fail file_ram_open() right away, similarly
to how we now fail if the file does not exist and we want to open the
file readonly.
With this change, we get a nicer error message:
qemu-system-x86_64: can't open backing store tmp for guest RAM: Is a directory
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().
Message-ID: <20230906120503.359863-8-david@redhat.com>
Reported-by: Thiner Logoer <logoerthiner1@163.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 138402b..f1cd3ec 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -1299,6 +1299,25 @@
for (;;) {
fd = open(path, readonly ? O_RDONLY : O_RDWR);
if (fd >= 0) {
+ /*
+ * open(O_RDONLY) won't fail with EISDIR. Check manually if we
+ * opened a directory and fail similarly to how we fail ENOENT
+ * in readonly mode. Note that mkstemp() would imply O_RDWR.
+ */
+ if (readonly) {
+ struct stat file_stat;
+
+ if (fstat(fd, &file_stat)) {
+ close(fd);
+ if (errno == EINTR) {
+ continue;
+ }
+ return -errno;
+ } else if (S_ISDIR(file_stat.st_mode)) {
+ close(fd);
+ return -EISDIR;
+ }
+ }
/* @path names an existing file, use it */
break;
}
