On Tue, 12 Sep 2000, Daniel Phillips wrote:
> Chris Mason wrote:
> > > Now I can unmerge this way:
> > >
> > > - Fix up various inode fields
> > > - getpage the tail page from the mapping
> > > - bread the shared tail block
> > > - get the appropriate page buffer using page_buffer
> > > - copy the tail fragment to that buffer and dirty it
> > >
> > > I can do this at a high level - the place where the unmerge conditions
> > > are most easily and accurately detected - as opposed to deep in the
> > > guts of the page I/O. The page is left in a state that already makes
> > > sense to read_page, write_page and friends.
> >
> > Sorry, I don't see how this saves you from the file size changing in
> > file_write or truncate. While you are breading the tail, file_write might
> > be trying to unmerge it.
>
> But this *is* unmerge. Clearly, I can't allow two unmerges at the
> same time on the same file. I haven't gotten to the locking yet, but
> this *must* be enforced one way or another.
Do it in ->prepare_write() if page is the last one. End of story. You'll
have to call the thing in your truncate() (expanding case) and that's it.
Pageout _never_ changes the file size, write and truncate own the ->i_sem.
So "page covers the end of file" is not going to change under you when you
are interested in unmerging. Here's your serialization.
-
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to [EMAIL PROTECTED]
