On 1/7/2025 5:01 AM, David Hildenbrand wrote:
On 02.01.25 22:32, Steve Sistare wrote:
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,
Note that offset is of type "off_t", not ram_addr_t.
ram_addr_t is a uintptr_t, but off_t can be a different integer type.
In meson.build we use "-D_FILE_OFFSET_BITS=64". So on 32bit ram_addr_t would be
32bit but off_t will be 64bit.
Printing off_t can be weird [1]. Maybe just cast it to an uint64_t and print it
using PRIx64?
I will fix as you suggest, thanks. Good catch.
With that, should I add your ack or RB to V3?
- Steve
[1]
https://stackoverflow.com/questions/586928/how-should-i-print-types-like-off-t-and-size-t
