Re: tux as ftp server question

On Tue, 2 Apr 2002, zhang li wrote:

> Tux reference says tux as FTP server is implemented
> totally in kernel(a C module of 900 lines). So I am
> wondering what's the use of zero-copy in it. It seems
> there is no copy between user-space and kernel-space
> at all, right?

correct. For sending files, TUX/FTP uses zero-copy, just
like TUX/HTTP does.

in fact TUX/FTP and TUX/HTTP share much code, it's mostly
the protocol decoding that needs to go into proto_ftp.c
and proto_http.c. Eg. the 'send file' logic is shared as
well.

> Even if we consider ftp server reads data from a file
> on the disk(when ftp client announce "get" command),
> the data will be put in kernel buffer directly after
> being read, right? So what's the use of zero-copy in
> Tux ftp server?

if the file is already cached (it's a frequently accessed
file) then TUX will send the file contents to the network
without doing any copying.

when reading the file contents into RAM from disk, then
TUX [well, the Linux kernel] will DMA it from disk into
RAM straight, without the CPU having to copy the data.

	Ingo