On 09/30/2013 08:02 PM, Myklebust, Trond wrote:
On Mon, 2013-09-30 at 19:48 +0200, Bernd Schubert wrote:
On 09/30/2013 07:44 PM, Myklebust, Trond wrote:
On Mon, 2013-09-30 at 19:17 +0200, Bernd Schubert wrote:
It would be nice if there would be way if the file system would get a
hint that the target file is supposed to be copy of another file. That
way distributed file systems could also create the target-file with the
correct meta-information (same storage targets as in-file has).
Well, if we cannot agree on that, file system with a custom protocol at
least can detect from 0 to SSIZE_MAX and then reset metadata. I'm not
sure if this would work for pNFS, though.
splice() does not create new files. What you appear to be asking for
lies way outside the scope of that system call interface.
Sorry I know, definitely outside the scope of splice, but in the context
of offloaded file copies. So the question is, what is the best way to
address/discuss that?
Why does it need to be addressed in the first place?
An offloaded copy is still not efficient if different storage
servers/targets used by from-file and to-file.
What is preventing an application from retrieving and setting this
information using standard libc functions such as fstat()+open(), and
supplemented with libattr attr_setf/getf(), and libacl acl_get_fd/set_fd
where appropriate?
At a minimum this requires network and metadata overhead. And while I'm
working on FhGFS now, I still wonder what other file system need to do -
for example Lustre pre-allocates storage-target files on creating a
file, so file layout changes mean even more overhead there.
Anyway, if we could agree on to use libattr or libacl to teach the file
system about the upcoming splice call I would be fine. Metadata overhead
is probably negligible for large files.
Thanks,
Bernd
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