@@ -1969,6 +1969,25 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
if (fd < 0) {
error_setg_errno(errp, -fd, "can't open backing store %s for guest RAM",
mem_path);
+ if (!(ram_flags & RAM_READONLY_FD) && !(ram_flags & RAM_SHARED) &&
+ fd == -EACCES) {
+ /*
+ * If we can open the file R/O (note: will never create a new file)
+ * and we are dealing with a private mapping, there are still ways
+ * to consume such files and get RAM instead of ROM.
+ */
+ fd = file_ram_open(mem_path, memory_region_name(mr), true,
+ &created);
+ if (fd < 0) {
+ return NULL;
+ }
+ assert(!created);
+ close(fd);
+ error_append_hint(errp, "Consider opening the backing store"
+ " read-only but still creating writable RAM using"
+ " '-object memory-backend-file,readonly=on,rom=off...'"
+ " (see \"VM templating\" documentation)\n");
+ }
return NULL;
}
It's easy to miss that memory-backend-file with "share=off" (default) will always try opening the file R/W as default, and fail if we don't have write permissions to the file. In that case, the user has to explicit specify "readonly=on,rom=off" to get usable RAM, for example, for VM templating. Let's hint that '-object memory-backend-file,readonly=on,rom=off,...' exists to consume R/O files in a private mapping to create writable RAM, but only if we have permissions to open the file read-only. Suggested-by: ThinerLogoer <logoerthiner1@163.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- softmmu/physmem.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)