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    SubjectRe: [PATCH 02/11] vfs: Add better VFS support for page_mkwrite when blocksize < pagesize
    On Thu, Jul 02, 2009 at 09:22:25AM +0200, Nick Piggin wrote:
    > > Looking at your patch I really like that vmtruncate now really just
    > > does what it's name claims to - truncate the VM-information about
    > > the file (well, and the file size). I'm not so happy about
    > > still keeping the two level setattr/truncate indirection.
    >
    > In my patch series, i_size update eventually is moved out to the
    > filesystem too, and vmtruncate just is renamed to truncate_pagecache
    > (vmtruncate is not such a bad name, but rename will nicely break
    > unconverted modules).

    Good, that's a much better calling and naming convention.

    > > But instead of folding truncate into setattr I wonder if we should
    > > just add a new ->setsize (aka new trunacte) methodas a top-level
    > > entry point instead of ->setattr with ATTR_SIZE given that size
    > > changes don't have much in common with the reset of ->setattr.
    >
    > OK that would be possible and makes sense I guess. The new truncate
    > which returns error could basically be renamed in-place. Shall we
    > continue to give ATTR_SIZE to setattr, or take that out completely?
    > I guess truncate can be considered special because it operates on
    > data not only metadata.
    >
    > Looks like ->setsize would need a flag for ATTR_OPEN too? Any others?
    > I'll do a bit of an audit when I get around to it...

    In the end ATTR_SIZE should not be passed to ->setattr anymore, and
    ->setsize should become mandatory. For the transition I would recommend
    calling ->setsize if present else fall back to the current way. That
    way we can migreate one filesystem per patch to the new scheme.

    I would suggest giving the flags to ->setsize their own namespace with
    two flags so far SETSIZE_FTRUNCATE (need to update the file size and
    have a file struct available) and SETSIZE_OPEN for the ATTR_OPEN case.

    That beeing said I reallye hate the conditiona file argument for
    ftrunctate (currently hidden inside struct iattr), maybe we're better
    off having am optional int (*ftruncate)(struct file *) method for those
    filesystems that need it, with a fallback to ->setsize.

    And yeah, maybe ->setsize might better be left as ->truncate, but if
    we want a nicely bisectable migration we'd have to rename the old
    truncate to e.g. ->old_truncate before. That's probably worth having
    the better naming in the end.



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