[systemd-devel] [PATCH] Partially revert "ma-setup: simplify"

[Lennart Poettering]

On Wed, 03.06.15 11:23, Mimi Zohar (zohar at linux.vnet.ibm.com) wrote:

> On Wed, 2015-06-03 at 06:50 +0200, Lennart Poettering wrote:
> > On Tue, 02.06.15 11:55, Mimi Zohar (zohar at linux.vnet.ibm.com) wrote:
> > 
> > > > We could add another parameter to copy_bytes(), but in this case it's
> > > > cleaner to call fstat() and loop_write().
> > > 
> > > Right.  copy_bytes has no concept of rules/records.  So either "another
> > > parameter" is added to copy_bytes to indicate skip try_sendfile and
> > > write the entire policy, or [partially] revert the patch to calll
> > > loop_write() to write the entire policy directly.
> > 
> > In which way does sendfile() fail here? I mean, the code currently
> > understands ENOSYS and EINVAL as indications that sendfile() is not
> > supported on an fd. What does sendfile() on the IMA device return?
> > Most likely we can just check for that error code, and then try the
> > loop as fallback.
> 
> After the sendfile failure, in addition to resetting the file position
> to the beginning of the file,  the file would also need to be closed and
> re-opened.   Otherwise, IMA assumes the policy was malformed and fails
> the policy update.

Why would the file position need to be reset? I mean, either the
sendfile() works or it doesn't. If it doesn't, then it should not
modify the fd's file position in any way.

Are you saying that sendfile() is really broken about this?

I really don't see why first trying sendfile(), then falling back to
read()/write() would not work. 

Can you elaborate?

Lennart

-- 
Lennart Poettering, Red Hat