Re: [RFC PATCH 2/3] add statmnt(2) syscall

[Miklos Szeredi]

On Tue, 26 Sept 2023 at 16:19, Florian Weimer <fweimer@xxxxxxxxxx> wrote:

> getdents gets away with this buffer size because applications can copy
> out all the data from struct dirent if they need long-term storage.
> They have to do that because the usual readdir interface overwrites the
> buffer, potentially at the next readdir call.  This means the buffer
> size does not introduce an amount of memory fragmention that is
> dependent on the directory size.
>
> With an opaque, pointer-carrying struct, copying out the data is not
> possible in a generic fashion.  Only the parts that the application
> knows about can be copied out.  So I think it's desirable to have a
> fairly exact allocation.

Okay, so let's add a 'size' field to the struct, which is set to the
size used (as opposed to the size of the buffer).   That should solve
copying without wasting a single byte of memory.

Otherwise the format is fully copyable, since the strings are denoted
with an offset, which doesn't change after the buffer is copied.

Thanks,
Miklos