Re: [PATCH] physmem: fix qemu_ram_alloc_from_fd size calculation

[Steven Sistare]

On 1/2/2025 4:14 PM, Peter Xu wrote:
> On Thu, Jan 02, 2025 at 12:34:50PM -0800, 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
>
> Can have the cc tag here too to be super clear:
>
> Cc: qemu-stable@nongnu.org

Done and resubmitted.

> > Fixes: 4b870dc4d0c0 ("hostmem-file: add offset option")
> > Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>
> Reviewed-by: Peter Xu <peterx@redhat.com>
>
> Please also feel free to attach this patch as the 1st patch when repost
> cpr-transfer, it could make dependency easier no matter how this would
> land.

Will do - steve

> Maybe it'll be still easier to go via a migration pull that collects cpr
> transfer as a whole. May depend on whether there'll be a memory API pull
> before that..