Re: [PATCH v4 0/7] kernel tinification: optionally compile out splice family of syscalls (splice, vmsplice, tee and sendfile)

[josh@joshtriplett.org]

[Resending this mail due to some email encoding brokenness that
prevented it from reaching LKML the first time; sorry to anyone who
receives two copies.]

On Tue, Nov 25, 2014 at 08:17:58AM -0800, Randy Dunlap wrote:
> On 11/24/2014 03:00 PM, Pieter Smith wrote:
> >REPO: https://github.com/smipi1/linux-tinification.git
> >
> >BRANCH: tiny/config-syscall-splice
> >
> >BACKGROUND: This patch-set forms part of the Linux Kernel Tinification effort (
> >   https://tiny.wiki.kernel.org/).
> >
> >GOAL: Support compiling out the splice family of syscalls (splice, vmsplice,
> >   tee and sendfile) along with all supporting infrastructure if not needed.
> >   Many embedded systems will not need the splice-family syscalls. Omitting them
> >   saves space.
> 
> Hi,
> 
> Is the splice family of syscalls the only one that tiny has identified
> for optional building or can we expect similar treatment for other
> syscalls?

Pretty much any system call that you could conceive of writing a
userspace without.

There's a partial project list at https://tiny.wiki.kernel.org/projects.

> Why will many embedded systems not need these syscalls?  You know
> exactly what apps they run and you are positive that those apps do
> not use splice?

Yes, precisely.  We're talking about embedded systems small enough that
you're booting with init=/your/app and don't even call fork(), where you
know exactly what code you're putting in and what libraries you use.
And they're almost certainly not running glibc.

> >RESULTS: A tinyconfig bloat-o-meter score for the entire patch-set:
> >
> >add/remove: 0/41 grow/shrink: 5/7 up/down: 23/-8422 (-8399)
> 
> The summary is that this patch saves around 8 KB of code space --
> is that correct?

Right.  For reference, we're talking about kernels where the *total*
size is a few hundred kB.

> How much storage space do embedded systems have nowadays?

For the embedded systems we're targeting for the tinification effort, in
a first pass: 512k-2M of storage (often for an *uncompressed* kernel, to
support execute-in-place), and 128k-512k of memory.  We've successfully
built useful kernels and userspaces for such environments, and we'd like
to go even smaller.

- Josh Triplett