linux-kernel - Re: [PATCH] Document genhd capability flags

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Date:   Sun, 8 Mar 2020 22:58:12 +0100
From:   Stephen Kitt <steve@....org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Document genhd capability flags

[Re-send, apparently this didn’t make it out of my computer.]

On Fri, 6 Mar 2020 09:23:09 -0800, Matthew Wilcox <willy@...radead.org> wrote:
> On Fri, Mar 06, 2020 at 06:16:21PM +0100, Stephen Kitt wrote:
> > The kernel documentation includes a brief section about genhd
> > capabilities, but it turns out that the only documented
> > capability (GENHD_FL_MEDIA_CHANGE_NOTIFY) isn't used any more.
> > 
> > This patch removes that flag, and documents the rest, based on my
> > understanding of the current uses of these flags in the kernel. The
> > documentation is kept in the header file, alongside the declarations,
> > in the hope that it will be kept up-to-date in future; the kernel
> > documentation is changed to include the documentation generated from
> > the header file.
> > 
> > Because the ultimate goal is to provide some end-user
> > documentation (or end-administrator documentation), the comments are
> > perhaps more user-oriented than might be expected.  
> 
> Thank you!  I have some suggestions for further improvement ...

Thanks for the quick review and the suggestions!

> > -capability is a hex word indicating which capabilities a specific disk
> > -supports.  For more information on bits not listed here, see
> > -include/linux/genhd.h
> > +``capability`` is a hex word indicating which capabilities a specific
> > +disk supports:  
> 
> ``capability`` is a bitfield, printed in hexadecimal, indicating ...
> 
> > + * ``GENHD_FL_UP`` (16): indicates that the block device is "up", with
> > + * a similar meaning to network interfaces.  
> 
> Since we're printing it in hex, the value here should be displayed in hex
> to help the end-user.  So ``GENHD_FL_UP`` (0x10), etc.
> 
> >  #define GENHD_FL_REMOVABLE			1
> > -/* 2 is unused */
> > -#define GENHD_FL_MEDIA_CHANGE_NOTIFY		4
> > +/* 2 is unused (used to be GENHD_FL_DRIVERFS) */
> > +/* 4 is unused (used to be GENHD_FL_MEDIA_CHANGE_NOTIFY) */
> >  #define GENHD_FL_CD				8
> >  #define GENHD_FL_UP				16
> >  #define GENHD_FL_SUPPRESS_PARTITION_INFO	32
> > -#define GENHD_FL_EXT_DEVT			64 /* allow extended
> > devt */ +#define GENHD_FL_EXT_DEVT			64
> >  #define GENHD_FL_NATIVE_CAPACITY		128
> >  #define GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE	256
> >  #define GENHD_FL_NO_PART_SCAN			512  
> 
> Maybe these should also be converted to hex to match?

Yes, these are all excellent ideas, I’ll follow up with a v2 (also updating
the terminology in capability.rst since this is about block devices, not only
disks).

Regards,

Stephen

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