[PATCH] O_NOATIME support for open(2)

[Daniel Roethlisberger]

I'm trying to implement O_NOATIME support for open(2) in order to
provide a more elegant way for backup/archiving software to
prevent atime clobbering.  Except for a 2008 thread on this list
I did not find any material; not sure if anybody is interested in
this or if there are reasons why this was never implemented.

The attached patch against 11.1 implements O_NOATIME support for
open(2); it prevents read(2) and mmap(2) from clobbering atime if
the file descriptor was opened with O_NOATIME.  O_NOATIME is only
permitted for root and the owner of the file.  Currently it is
only implemented for ufs/ffs.  It seems to work for me but has
not been extensively tested.

I am interested in feedback from people who know their way around
I/O and VFS code before I extend this to other file systems, make
O_NOATIME tunable by fcntl(2), wire it to the Linux compat layer
and write docs.  Does the implementation look sane?  Did I miss
something important?

Specifically, is there a better way to pass O_NOATIME into
vm_mmap_vnode other than adding an additional boolean_t argument?
I did not use an additional mmap flag because that would have
required additional logic to prevent userland from passing the
flag to the mmap syscall.

Daniel

-- 
Daniel Roethlisberger
http://daniel.roe.ch/

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