On Tue, Nov 25, 2014 at 08:17:58AM -0800, Randy Dunlap wrote:

On 11/24/2014 03:00 PM, Pieter Smith wrote:

quoted

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.

quoted

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

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