Re: [PATCH v2] xfs_scrub: don't use statvfs to collect filesystem summary counts

Darrick J. Wong
2020-10-09T15:39:47Z

On Fri, Oct 09, 2020 at 07:32:25AM -0400, Brian Foster wrote:
> On Fri, Oct 09, 2020 at 07:18:12AM -0400, Brian Foster wrote:
> > On Mon, Oct 05, 2020 at 09:37:37AM -0700, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > >
> > > The function scrub_scan_estimate_blocks naÃƒÂ¯vely uses the statvfs counts
> > > to estimate the size and free blocks on the data volume. Unfortunately,
> > > it fails to account for the fact that statvfs can return the size and
> > > free counts for the realtime volume if the root directory has the
> > > rtinherit flag set, which leads to phase 7 reporting totally absurd
> > > quantities.
> > >
> > > Eric pointed out a further problem with statvfs, which is that the file
> > > counts are clamped to the current user's project quota inode limits.
> > > Therefore, we must not use statvfs for querying the filesystem summary
> > > counts.
> > >
> > > The XFS_IOC_FSCOUNTS ioctl returns all the data we need, so use that
> > > instead.
> > >
> > > Fixes: 604dd3345f35 ("xfs_scrub: filesystem counter collection functions")
> > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > ---
> > > v2: drop statvfs entirely
> > > ---
> >
> > This doesn't seem to apply to for-next..?
> >
>
> Oops, never mind. Wrong tree...
>
>
> > Brian
> >
> > > scrub/fscounters.c | 27 ++++-----------------------
> > > 1 file changed, 4 insertions(+), 23 deletions(-)
> > >
> > > diff --git a/scrub/fscounters.c b/scrub/fscounters.c
> > > index f9d64f8c008f..e9901fcdf6df 100644
> > > --- a/scrub/fscounters.c
> > > +++ b/scrub/fscounters.c
> > > @@ -130,38 +130,19 @@ scrub_scan_estimate_blocks(
> > > unsigned long long *f_free)
> > > {
> > > struct xfs_fsop_counts fc;
> > > - struct xfs_fsop_resblks rb;
> > > - struct statvfs sfs;
> > > int error;
> > >
> > > - /* Grab the fstatvfs counters, since it has to report accurately. */
> > > - error = fstatvfs(ctx->mnt.fd, &sfs);
> > > - if (error)
> > > - return errno;
> > > -
> > > /* Fetch the filesystem counters. */
> > > error = ioctl(ctx->mnt.fd, XFS_IOC_FSCOUNTS, &fc);
> > > if (error)
> > > return errno;
> > >
> > > - /*
> > > - * XFS reserves some blocks to prevent hard ENOSPC, so add those
> > > - * blocks back to the free data counts.
> > > - */
> > > - error = ioctl(ctx->mnt.fd, XFS_IOC_GET_RESBLKS, &rb);
> > > - if (error)
> > > - return errno;
> > > -
> > > - sfs.f_bfree += rb.resblks_avail;
> > > -
> > > - *d_blocks = sfs.f_blocks;
> > > - if (ctx->mnt.fsgeom.logstart > 0)
> > > - *d_blocks += ctx->mnt.fsgeom.logblocks;
> > > - *d_bfree = sfs.f_bfree;
> > > + *d_blocks = ctx->mnt.fsgeom.datablocks;
> > > + *d_bfree = fc.freedata;
> > > *r_blocks = ctx->mnt.fsgeom.rtblocks;
> > > *r_bfree = fc.freertx;
> > > - *f_files = sfs.f_files;
> > > - *f_free = sfs.f_ffree;
> > > + *f_files = fc.allocino;
> > > + *f_free = fc.freeino;
> > >
>
> Aren't the free inode counters semantically different between statvfs
> and this ioctl? I thought stat had some logic to effectively show free
> data blocks as free inodes,

It does.

> whereas the ioctl looks like it just reads
> our internal counter (which IIRC is a subset of physically allocated
> inode chunks). Do we care about that semantic here either way?

Nope. The one caller that cares (scrub/phase7.c) only wants to know the
number of inodes in use (f_free - f_files), which is unaffected by the
logic in xfs_fs_statfs.

I suppose I could trim the parameter list even further to return only
the file count...

--D

> Brian
>
> > > return 0;
> > > }
> > >
> >
>