linux-kernel - Re: [PATCH v7 10/11] xfs: make the calculation generic in xfs_sb_validate_fsb

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Date: Mon, 17 Jun 2024 16:09:37 +0000
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Christoph Hellwig <hch@....de>
Cc: david@...morbit.com, djwong@...nel.org, chandan.babu@...cle.com,
	brauner@...nel.org, akpm@...ux-foundation.org, willy@...radead.org,
	mcgrof@...nel.org, linux-mm@...ck.org, hare@...e.de,
	linux-kernel@...r.kernel.org, yang@...amperecomputing.com,
	Zi Yan <zi.yan@...t.com>, linux-xfs@...r.kernel.org,
	p.raghav@...sung.com, linux-fsdevel@...r.kernel.org,
	gost.dev@...sung.com, cl@...amperecomputing.com,
	john.g.garry@...cle.com
Subject: Re: [PATCH v7 10/11] xfs: make the calculation generic in
 xfs_sb_validate_fsb_count()

On Thu, Jun 13, 2024 at 10:45:45AM +0200, Christoph Hellwig wrote:
> > +	uint64_t		max_index;
> > +	uint64_t		max_bytes;
> > +
> >  	ASSERT(PAGE_SHIFT >= sbp->sb_blocklog);
> >  	ASSERT(sbp->sb_blocklog >= BBSHIFT);
> >  
> > +	if (check_shl_overflow(nblocks, sbp->sb_blocklog, &max_bytes))
> > +		return -EFBIG;
> > +
> >  	/* Limited by ULONG_MAX of page cache index */
> > -	if (nblocks >> (PAGE_SHIFT - sbp->sb_blocklog) > ULONG_MAX)
> > +	max_index = max_bytes >> PAGE_SHIFT;
> > +
> > +	if (max_index > ULONG_MAX)
> 
> Do we really need the max_index variable for a single user here?
> Or do you plan to add more uses of it later (can't really think of one
> though)?

Yeah, we could just inline it:

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index a99454208807..c6933440f806 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -132,7 +132,6 @@ xfs_sb_validate_fsb_count(
        xfs_sb_t        *sbp,
        uint64_t        nblocks)
 {
-       uint64_t                max_index;
        uint64_t                max_bytes;
 
        ASSERT(sbp->sb_blocklog >= BBSHIFT);
@@ -141,9 +140,7 @@ xfs_sb_validate_fsb_count(
                return -EFBIG;
 
        /* Limited by ULONG_MAX of page cache index */
-       max_index = max_bytes >> PAGE_SHIFT;
-
-       if (max_index > ULONG_MAX)
+       if (max_bytes >> PAGE_SHIFT > ULONG_MAX)
                return -EFBIG;
        return 0;
 }

>