[RFC PATCH] nvmet: Make blksize_shift configurable

[Richard Weinberger]

On Freitag, 18. April 2025 11:37 'Damien Le Moal' via upstream wrote:
> > +	if (!ns->blksize_shift)
> > +		ns->blksize_shift = blksize_bits(bdev_logical_block_size(ns->bdev));
> 
> If the user set logical block size is smaller than the block dev logical block
> size, this is not going to work... No ? Am I missing something ?

Likely, yes.
TBH, I'm not sure whether it makes actually sense for the bdev case to make
blksize_shift configurable.
The case I see most benefit is the backing file case.

> > +	if (!ns->blksize_shift) {
> > +		/*
> > +		 * i_blkbits can be greater than the universally accepted
> > +		 * upper bound, so make sure we export a sane namespace
> > +		 * lba_shift.
> > +		 */
> > +		ns->blksize_shift = min_t(u8,
> > +				file_inode(ns->file)->i_blkbits, 12);
> 
> This will work for any block size, regardless of the FS block size, but only if
> ns->buffered_io is true. Doesn't this require some more checks with regards to
> O_DIRECT (!ns->buffered_io case) ?

Good catch. I'll add a check.

It's also worth discussing whether we should limit blksize_shift to a specific
range. Right now, any shift is accepted, and it is up to the user to
use a sane value.

Thanks,
//richard

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