Re: [PATCH 1/2] scsi: target: core: Add sense reason for space allocation errors

[Konstantin Shelekhin <k.shelekhin@yadro.com>]

On Wed, Oct 20, 2021 at 11:21:54PM -0400, Martin K. Petersen wrote:
> 
> Konstantin,
> 
> > According to SBC-3 4.7.3.6 this sense reason shall be used in situations
> > where thin provisioned logical unit cannot satisfy the write request due
> > to the lack of free blocks.
> 
> > +	[TCM_SPACE_ALLOCATION_FAILED] = {
> > +		.key = DATA_PROTECT,
> > +		.asc = 0x27,
> > +		.ascq = 0x07, /* SPACE ALLOCATION FAILED WRITE PROTECT */
> > +	},
> 
> How do we know this is a permanent condition and not a temporary space
> exhaustion?

By permanent condition SBC-3 means that an initiator should not resend
the command immediately as it will fail again. Kernel tries hard not to
fail with BLK_STS_NOSPC:

  /*
   * We're holding onto IO to allow userland time to react.  After the
   * timeout either the pool will have been resized (and thus back in
   * PM_WRITE mode), or we degrade to PM_OUT_OF_DATA_SPACE w/ error_if_no_space.
   */
  static void do_no_space_timeout(struct work_struct *ws)

So BLK_STS_NOSPC means that we are stuck with this condition and some
out-of-scope actions (like running fs-trim on the initiator) are
required.