Re: [PATCH] generic/466: be more precise about which block sizes to use

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Sun, Dec 31, 2017 at 01:45:08PM -0500, Theodore Ts'o wrote:
> On Wed, Dec 13, 2017 at 09:36:29AM -0800, Darrick J. Wong wrote:
> > > +	get_page_size
> > > +	;;
> > > +    *)
> > > +	echo 512
> > 
> > FWIW XFS' minimum block size is 1k for v5 filesystems, though you can't
> > really tell until you run mkfs.xfs -N.
> 
> Ok, but I assume we should keep this at 512 since it could be a v4
> file systems that are being tested?

That depends on whether this function returns the smallest blocksize
guaranteed to pass mkfs given the current set of options or the
theoretical smallest blocksize supported by that fs given the right set
of options.  IOWs, if this is a v5 fs being tested, then "mkfs.xfs -b
size=$(_fs_min_blocksize) -m crc=1" will fail.

> > > +_fs_max_blocksize()
> > > +{
> > > +    get_page_size
> > 
> > Also, one can run xfstests against a fuse2fs-mounted 64k-block ext4 fs.
> 
> Really?  Does mmap work on a fuse2fs-mounted 64k-block ext4 file system?

Yes:

# uname -a
Linux magnolia 4.14.8-67-magnolia #2 SMP PREEMPT Fri Dec 22 17:23:52 PST 2017 x86_64 x86_64 x86_64 GNU/Linux
# truncate -s 1g /tmp/a
# mkfs.ext4 -b 65536 -F /tmp/a
...
# fuse2fs /tmp/a /mnt
/tmp/a: Writing to the journal is not supported.
# fallocate -l 128k /mnt/a
# xfs_io -c 'mmap -rw 0 128k' -c 'mwrite -S 0x58 0 6144' /mnt/a
# od -tx1 -Ad -c /mnt/a
0000000  58  58  58  58  58  58  58  58  58  58  58  58  58  58  58  58
          X   X   X   X   X   X   X   X   X   X   X   X   X   X   X   X
*
0006144  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00
         \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0131072

> I suppose can just force the block size to be 64k for fuse2fs,
> although I don't think the using some file system like ext4 for
> fuse2fs testing isn't going to work right now anyway, yes?

I haven't tried it in some time, but the last time I ran xfstests
against fuse2fs it more or less worked (modulo all the fancy fallocate
stuff that it doesn't support).

--D

> 
> 	      	   	     		     	       - Ted