Re: [PATCH 1/2] scsi: sd: Separate zeroout and discard command choices

["hch@lst.de" <hch@lst.de>]

On Fri, Apr 07, 2017 at 07:59:08PM +0000, Bart Van Assche wrote:
> On Wed, 2017-04-05 at 07:41 -0400, Martin K. Petersen wrote:
> > +static ssize_t
> > +zeroing_mode_store(struct device *dev, struct device_attribute *attr,
> > +		   const char *buf, size_t count)
> > +{
> > +	struct scsi_disk *sdkp = to_scsi_disk(dev);
> > +
> > +	if (!capable(CAP_SYS_ADMIN))
> > +		return -EACCES;
> > +
> > +	if (!strncmp(buf, zeroing_mode[SD_ZERO_WRITE], 20))
> > +		sdkp->zeroing_mode = SD_ZERO_WRITE;
> > +	else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS], 20))
> > +		sdkp->zeroing_mode = SD_ZERO_WS;
> > +	else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS16_UNMAP], 20))
> > +		sdkp->zeroing_mode = SD_ZERO_WS16_UNMAP;
> > +	else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS10_UNMAP], 20))
> > +		sdkp->zeroing_mode = SD_ZERO_WS10_UNMAP;
> > +	else
> > +		return -EINVAL;
> > +
> > +	return count;
> > +}
> 
> An additional question about this function: if the shell command "echo" is used
> without command-line option -n to modify the "zeroing_mode" sysfs attribute then
> a newline character will be present in buf. Does the above code handle newline
> characters correctly?

It ignores the newlines.  But we have a helper called sysfs_streq
to possible ignore it.  It might be a good idea to move the various
sysfs files in scsi to use it.