qemu_ram_alloc_from_fd allocates space if file_size == 0. If non-zero, it uses the existing space and verifies it is large enough, but the verification was broken when the offset parameter was introduced. As a result, a file smaller than offset passes the verification and causes errors later. Fix that, and update the error message to include offset.
Peter provides this concise reproducer: $ touch ramfile $ truncate -s 64M ramfile $ ./qemu-system-x86_64 -object memory-backend-file,mem-path=./ramfile,offset=128M,size=128M,id=mem1,prealloc=on qemu-system-x86_64: qemu_prealloc_mem: preallocating memory failed: Bad address With the fix, the error message is: qemu-system-x86_64: mem1 backing store size 0x4000000 is too small for 'size' option 0x8000000 plus 'offset' option 0x8000000 Cc: qemu-sta...@nongnu.org Fixes: 4b870dc4d0c0 ("hostmem-file: add offset option") Signed-off-by: Steve Sistare <steven.sist...@oracle.com> Reviewed-by: Peter Xu <pet...@redhat.com> --- system/physmem.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/system/physmem.c b/system/physmem.c index c76503a..f01325f 100644 --- a/system/physmem.c +++ b/system/physmem.c @@ -1970,10 +1970,11 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr, size = REAL_HOST_PAGE_ALIGN(size); file_size = get_file_size(fd); - if (file_size > offset && file_size < (offset + size)) { - error_setg(errp, "backing store size 0x%" PRIx64 - " does not match 'size' option 0x" RAM_ADDR_FMT, - file_size, size); + if (file_size && file_size < offset + size) { + error_setg(errp, "%s backing store size 0x%" PRIx64 + " is too small for 'size' option 0x" RAM_ADDR_FMT + " plus 'offset' option 0x" RAM_ADDR_FMT, + memory_region_name(mr), file_size, size, offset); return NULL; } -- 1.8.3.1