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Re: [PATCH V3] ieee1275: obdisk driver

From: Daniel Kiper
Subject: Re: [PATCH V3] ieee1275: obdisk driver
Date: Wed, 6 Mar 2019 12:32:55 +0100
User-agent: NeoMutt/20170113 (1.7.2)

On Mon, Mar 04, 2019 at 05:27:39PM -0800, Eric Snowberg wrote:
> Add a new disk driver called obdisk for IEEE1275 platforms.  Currently
> the only platform using this disk driver is SPARC, however other IEEE1275
> platforms could start using it if they so choose.  While the functionality
> within the current IEEE1275 ofdisk driver may be suitable for PPC and x86, it
> presented too many problems on SPARC hardware.
> Within the old ofdisk, there is not a way to determine the true canonical
> name for the disk.  Within Open Boot, the same disk can have multiple names
> but all reference the same disk.  For example the same disk can be referenced
> by its SAS WWN, using this form:
> /address@hidden/address@hidden/address@hidden/address@hidden/LSI,address@hidden/address@hidden,0
> It can also be referenced by its PHY identifier using this form:
> /address@hidden/address@hidden/address@hidden/address@hidden/LSI,address@hidden/address@hidden
> It can also be referenced by its Target identifier using this form:
> /address@hidden/address@hidden/address@hidden/address@hidden/LSI,address@hidden/address@hidden
> Also, when the LUN=0, it is legal to omit the ,0 from the device name.  So 
> with
> the disk above, before taking into account the device aliases, there are 6 
> ways
> to reference the same disk.
> Then it is possible to have 0 .. n device aliases all representing the same 
> disk.
> Within this new driver the true canonical name is determined using the the
> IEEE1275 encode-unit and decode-unit commands when address_cells == 4.  This
> will determine the true single canonical name for the device so multiple 
> ihandles
> are not opened for the same device.  This is what frequently happens with the 
> old
> ofdisk driver.  With some devices when they are opened multiple times it 
> causes
> the entire system to hang.
> Another problem solved with this driver is devices that do not have a device
> alias can be booted and used within GRUB. Within the old ofdisk, this was not
> possible, unless it was the original boot device.  All devices behind a SAS
> or SCSI parent can be found.   Within the old ofdisk, finding these disks
> relied on there being an alias defined.  The alias requirement is not
> necessary with this new driver.  It can also find devices behind a parent
> after they have been hot-plugged.  This is something that is not possible
> with the old ofdisk driver.
> The old ofdisk driver also incorrectly assumes that the device pointing to by 
> a
> device alias is in its true canonical form. This assumption is never made with
> this new driver.
> Another issue solved with this driver is that it properly caches the ihandle
> for all open devices.  The old ofdisk tries to do this by caching the last
> opened ihandle.  However this does not work properly because the layer above
> does not use a consistent device name for the same disk when calling into the
> driver.  This is because the upper layer uses the bootpath value returned 
> within
> /chosen, other times it uses the device alias, and other times it uses the
> value within grub.cfg.  It does not have a way to figure out that these 
> devices
> are the same disk.  This is not a problem with this new driver.
> Due to the way GRUB repeatedly opens and closes the same disk. Caching the
> ihandle is important on SPARC.  Without caching, some SAS devices can take
> 15 - 20 minutes to get to the GRUB menu. This ihandle caching is not possible
> without correctly having the canonical disk name.
> When available, this driver also tries to use the deblocker #blocks and
> a way of determining the disk size.
> Finally and probably most importantly, this new driver is also capable of
> seeing all partitions on a GPT disk.  With the old driver, the GPT
> partition table can not be read and only the first partition on the disk
> can be seen.
> Signed-off-by: Eric Snowberg <address@hidden>

In the general I am OK with the patch but...

> ---
> Changes since V2 (all requested in the last review):
> Changed all if (x) to if (x != NULL)
> Removed static NULL initializations
> Removed all code to allow a user to easily retrieve the disk name thru the
> shell without needing to understand the grub2 escaping policy for
> disk names with commas. SPARC disks frequently contain commas, figuring
> this out is now up to the user. Cut and pasting the disk name is no
> longer possible. Also, this will make automated testing thru the shell
> extremely difficult.
> Changed the order of the functions to escape_commas(),
> replace_escaped_commas(), and finally count_commas().

... I am a bit confused with this. You left escape_commas() and
count_commas(). Both are used in encode_grub_devname(). IMO this does
not agree with "Removed all code to allow a user to easily retrieve the
disk name thru the shell without needing to understand the grub2
escaping policy for disk names with commas." Does it?


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