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From: Javier Gonz??lez <javier.gonz@samsung.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Minwoo Im <minwoo.im.dev@gmail.com>,
	Keith Busch <kbusch@kernel.org>, Sagi Grimberg <sagi@grimberg.me>,
	Kanchan Joshi <joshiiitr@gmail.com>,
	<linux-nvme@lists.infradead.org>
Subject: Re: [PATCH 13/13] nvme: introduce generic per-namespace chardev
Date: Mon, 12 Apr 2021 13:52:46 +0200	[thread overview]
Message-ID: <20210412115246.ocqdoejpfiswajqu@mpHalley.localdomain> (raw)
In-Reply-To: <20210412074455.GA3653@lst.de>

On 12.04.2021 09:44, Christoph Hellwig wrote:
>On Fri, Apr 09, 2021 at 08:24:01PM +0900, Minwoo Im wrote:
>> I think if we don't have a route to the live controller from the
>> multipath node /dev/ng0n1, how does application figure out controller
>> node to request admin commands like Identify Namespace before their
>> own I/O ?
>>
>> We have sysfs, but it does not provide every information about the
>> namespace.  Or is there any charming way to find out the live
>> controller from a head node through sysfs or something that I missed
>> here ? :)
>
>The devie links points to the subsystem, which then points to the
>controllers:
>
>root@testvm:/sys/class/nvme-generic/ng0n1# ls -l device/
>total 0
>-r--r--r-- 1 root root 4096 Apr 12 07:43 firmware_rev
>-rw-r--r-- 1 root root 4096 Apr 12 07:44 iopolicy
>-r--r--r-- 1 root root 4096 Apr 12 07:43 model
>drwxr-xr-x 3 root root    0 Apr 12 07:43 ng0n1
>drwxr-xr-x 3 root root    0 Apr 12 07:43 ng0n2
>lrwxrwxrwx 1 root root    0 Apr 12 07:44 nvme0 -> ../../nvme-fabrics/ctl/nvme0
>drwxr-xr-x 9 root root    0 Apr 12 07:43 nvme0n1
>drwxr-xr-x 9 root root    0 Apr 12 07:43 nvme0n2
>lrwxrwxrwx 1 root root    0 Apr 12 07:44 nvme1 -> ../../nvme-fabrics/ctl/nvme1
>drwxr-xr-x 2 root root    0 Apr 12 07:44 power
>-r--r--r-- 1 root root 4096 Apr 12 07:43 serial
>-r--r--r-- 1 root root 4096 Apr 12 07:44 subsysnqn
>lrwxrwxrwx 1 root root    0 Apr 12 07:43 subsystem -> ../../../../class/nvme-subsystem
>-rw-r--r-- 1 root root 4096 Apr 12 07:43 uevent
>

It seems like a limitation that we have to transverse sysfs to make an
in-application enumeration to submit namespace-specific admin commands.

Ideally, applications that are already using IOCTLs should be able to
directly work with the char device. If this is not the case, I am afraid
that the applicability will be limited.

I understand that identifying the live controller in multipath is
something that we need to improve. The question is that if this is a
reasonable thing for you. If there is no fundamental limitation here, I
think we can work the details of enabling namespace admin commands
through and merge the same support for the block device and the char
device.

What do you think?

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  reply	other threads:[~2021-04-12 11:53 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20210408121108eucas1p1fb60de8498a7461b453295497c206246@eucas1p1.samsung.com>
2021-04-08 12:08 ` nvme ioctl refactor and generic per-namespace char device Christoph Hellwig
2021-04-08 12:08   ` [PATCH 01/13] nvme: add a nvme_ns_head_multipath helper Christoph Hellwig
2021-04-09  2:33     ` Chaitanya Kulkarni
2021-04-08 12:08   ` [PATCH 02/13] nvme: cleanup setting the disk name Christoph Hellwig
2021-04-08 12:08   ` [PATCH 03/13] nvme: pass a user pointer to nvme_nvm_ioctl Christoph Hellwig
2021-04-08 12:08   ` [PATCH 04/13] nvme: factor out a nvme_ns_ioctl helper Christoph Hellwig
2021-04-09  2:40     ` Chaitanya Kulkarni
2021-04-08 12:08   ` [PATCH 05/13] nvme: simplify the compat ioctl handling Christoph Hellwig
2021-04-09  2:42     ` Chaitanya Kulkarni
2021-04-09  5:39       ` Christoph Hellwig
2021-04-08 12:08   ` [PATCH 06/13] nvme: simplify block device ioctl handling for the !multipath case Christoph Hellwig
2021-04-08 12:08   ` [PATCH 07/13] nvme: don't bother to look up a namespace for controller ioctls Christoph Hellwig
2021-04-08 12:08   ` [PATCH 08/13] nvme: move the ioctl code to a separate file Christoph Hellwig
2021-04-09  2:45     ` Chaitanya Kulkarni
2021-04-08 12:08   ` [PATCH 09/13] nvme: factor out a nvme_tryget_ns_head helper Christoph Hellwig
2021-04-09  2:46     ` Chaitanya Kulkarni
2021-04-09  5:39       ` Christoph Hellwig
2021-04-09  5:40         ` Chaitanya Kulkarni
2021-04-09  9:18     ` Kanchan Joshi
2021-04-09  9:49       ` Christoph Hellwig
2021-04-08 12:08   ` [PATCH 10/13] nvme: move nvme_ns_head_ops to multipath.c Christoph Hellwig
2021-04-09  2:47     ` Chaitanya Kulkarni
2021-04-08 12:08   ` [PATCH 11/13] nvme: factor out nvme_ns_open and nvme_ns_release helpers Christoph Hellwig
2021-04-09  2:48     ` Chaitanya Kulkarni
2021-04-08 12:08   ` [PATCH 12/13] nvme: let namespace probing continue for unsupported features Christoph Hellwig
2021-04-08 22:42     ` Keith Busch
2021-04-09  5:39       ` Christoph Hellwig
2021-04-09  5:47         ` Keith Busch
2021-04-09  5:53           ` Christoph Hellwig
2021-04-08 12:08   ` [PATCH 13/13] nvme: introduce generic per-namespace chardev Christoph Hellwig
2021-04-08 16:56     ` Keith Busch
2021-04-08 17:00       ` Christoph Hellwig
2021-04-09  6:14       ` Christoph Hellwig
2021-04-09 14:29         ` Keith Busch
2021-04-09 14:35           ` Christoph Hellwig
2021-04-09  7:29     ` Minwoo Im
2021-04-09  7:54       ` Christoph Hellwig
2021-04-09  8:02         ` Minwoo Im
2021-04-09  9:52           ` Christoph Hellwig
2021-04-09 11:24             ` Minwoo Im
2021-04-12  7:44               ` Christoph Hellwig
2021-04-12 11:52                 ` Javier Gonz??lez [this message]
2021-04-08 22:43   ` nvme ioctl refactor and generic per-namespace char device Keith Busch
2021-04-09 17:45   ` Javier Gonz??lez
2021-04-10  6:46   ` Christoph Hellwig

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