On Fri, 2011-07-22 at 16:10 -0500, Alex Elder wrote:
> On Fri, 2011-07-22 at 13:49 -0700, Chandra Seetharaman wrote:
> > Thanks for the review Alex.
> >
> > See below for comments.
> >
> > On Fri, 2011-07-22 at 14:38 -0500, Alex Elder wrote:
> > > On Thu, 2011-07-21 at 17:32 -0700, Chandra Seetharaman wrote:
> > > > Remove the definitions and usage of the macros XFS_BUF_ERROR,
>
> . . .
Looking my message again, I think I may have gotten confused
along the way.
. . .
> > > > diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
> > > > index 88d1214..97daa35 100644
> > > > --- a/fs/xfs/xfs_vnodeops.c
> > > > +++ b/fs/xfs/xfs_vnodeops.c
> > > > @@ -83,7 +83,7 @@ xfs_readlink_bmap(
> > > >
> > > > bp = xfs_buf_read(mp->m_ddev_targp, d, BTOBB(byte_cnt),
> > > > XBF_LOCK | XBF_MAPPED | XBF_DONT_BLOCK);
> > >
> > > xfs_buf_read() can return NULL here, so to match
> > > the existing behavior you should call xfs_buf_geterror()
> > > here.
> > >
> > > > - error = XFS_BUF_GETERROR(bp);
> > > > + error = bp->b_error;
> > > > if (error) {
> > > > xfs_ioerror_alert("xfs_readlink",
> > > > ip->i_mount, bp, XFS_BUF_ADDR(bp));
> >
> > I did the change consciously. If bp were NULL, error would have been set
> > to ENOMEM, and xfs_ioerror_alert() and xfs_buf_relse(), would have
> > accessed bp and tripped anyways. So, I felt using the indirection
> > (xfs_buf_geterror()) is not adding any value, hence set error by
> > directly accessing b_error.
>
> But you are dereferencing a possibly null pointer in the
> code you added. Yes, the code that was already there
> should not dereference it either, but that's no excuse
> for you to do it. (And fix the other code while you're
> there, or make a note to get it fixed later.)
The comment above I stand by. But the next one I think
applies to another hunk of code.
In any case, hopefully you understand what my point
is and you'll be able to update your patch accordingly.
Sorry for the confusion.
-Alex
> The reason it's important here is that the value of error
> gets passed back to the caller, and although I didn't
> go very far back to see what effect it has, a quick look
> showed that it might lead to different behavior. As I
> said, it might be *correct* behavior, but in any case it's
> different, so it belongs in its own commit.
>
> > There are more place like these.
>
> I noticed you doing this sort of thing in a bunch of other
> spots in your patch, and in all of them they seemed to
> follow a test that ensured the buffer pointer was non-null
> (or it was implicit, because some *prior* dereference of
> the pointer would have been a problem) therefore simply
> checking bp->b_error was a fine replacement.
>
> But in this one spot, it's a bit different, so I called
> attention to it.
>
> If you are convinced I'm mistaken and this will produce
> results identical to before, say so and I'll take a
> closer look.
>
> > What do you think of this option
> >
> > Leave this as is (with b_error), and send another patch to check for bp
> > after xfs_buf_read() in all places (if you want this option, what do you
> > think error should be set to, I see both EIO and ENOMEM used. I think it
> > should be the same always).
> >
> > If you don't like that option I can revert to xfs_buf_geterror() too.
>
> I think using xfs_buf_geterror() is the easiest thing
> to do right now. Changing it such that xfs_readlink_bmap()
> returns ENOMEM in the event xfs_buf_read() here returns a null
> pointer sounds like a reasonable thing to do, but do it in
> a separate patch that focuses on that change and why it's
> correct. And (despite what I said earlier) I guess do it
> *after* we've got this series in. I'm about ready to get
> it committed once you get it updated.
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