[Qemu-devel] Re: [RFC][PATCH v5 07/21] virtagent: add va.getfile RPC

[Jes Sorensen]

On 12/03/10 19:03, Michael Roth wrote:
> Add RPC to retrieve a guest file. This interface is intended
> for smaller reads like peeking at logs and /proc and such.

I think you need to redesign your approach here..... see below.

In 06/21 you had:

+#define VA_GETFILE_MAX 1 << 30

> +    while ((ret = read(fd, buf, VA_FILEBUF_LEN)) > 0) {
> +        file_contents = qemu_realloc(file_contents, count + VA_FILEBUF_LEN);
> +        memcpy(file_contents + count, buf, ret);

UH OH!

realloc will do a malloc and a memcpy of the data, this is going to turn
into a really nasty malloc memcpy loop if someone tries to transfer a
large file using this method. You could end up with almost 4GB of
parallel allocations for a guest that might have been configured as a
1GB guest. This would allow the guest to effectively blow the expected
memory consumption out of the water. It's not exactly going to be fast
either :(

Maybe use a tmp file, and write data out to that as you receive it to
avoid the malloc ballooning.

Jes