Re: which dentry a page belongs to

[Jamie Lokier <jamie@shareable.org>]

Shaya Potter wrote:
> OK, great example, now I see the problem which can't be easily solved.
> 
> update-data
> ioctl
> update-data
> writepage()
> 
> writepage can't differentiate b/w data b4 and data after, so only way to
> do it would be to force a sync b4 ioctl is called, which I would think
> (perhaps wrong) should write out all the data to disk.  But unsure if
> prorgramatically able to really test to see if it worked or not.

"sync" doesn't do anything to help.

Read up on msync() until you understand what is intended here.

In general, first "update-data" in your example doesn't count as a
"write" and it wouldn't be logical for a program to expect it to be
snapshotted.  It counts as the program queuing up data which it does
not expect to be visible in the file until the next msync, munmap or
exit (although it is visible to other concurrent mmaps, and it _might_
be visible in the file, of parts of it might).

-- Jamie