linux-kernel - Re: [PATCH 1/2] cifs: client: force multichannel=off when max

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Message-ID: <qmf3xwqq4hqj4issgci2g76eghytaqxihnrp236ithh2istkkf@n4s54vp3hblr>
Date: Mon, 22 Sep 2025 11:59:37 -0300
From: Enzo Matsumiya <ematsumiya@...e.de>
To: Henrique Carvalho <henrique.carvalho@...e.com>
Cc: rajasimandalos@...il.com, linux-cifs@...r.kernel.org, 
	sfrench@...ba.org, pc@...guebit.org, ronniesahlberg@...il.com, 
	sprasad@...rosoft.com, tom@...pey.com, bharathsm@...rosoft.com, 
	linux-kernel@...r.kernel.org, Rajasi Mandal <rajasimandal@...rosoft.com>
Subject: Re: [PATCH 1/2] cifs: client: force multichannel=off when
 max_channels=1

On 09/22, Henrique Carvalho wrote:
>Hi Rajasi,
>
>On 9/22/25 5:24 AM, rajasimandalos@...il.com wrote:
>> From: Rajasi Mandal <rajasimandal@...rosoft.com>
>>
>> Previously, specifying both multichannel and max_channels=1 as mount
>> options would leave multichannel enabled, even though it is not
>> meaningful when only one channel is allowed. This led to confusion and
>> inconsistent behavior, as the client would advertise multichannel
>> capability but never establish secondary channels.
>>
>> Fix this by forcing multichannel to false whenever max_channels=1,
>> ensuring the mount configuration is consistent and matches user intent.
>> This prevents the client from advertising or attempting multichannel
>> support when it is not possible.
>>
>> Signed-off-by: Rajasi Mandal <rajasimandal@...rosoft.com>
>> ---
>>  fs/smb/client/fs_context.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
>> index 072383899e81..43552b44f613 100644
>> --- a/fs/smb/client/fs_context.c
>> +++ b/fs/smb/client/fs_context.c
>> @@ -1820,6 +1820,13 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
>>  		goto cifs_parse_mount_err;
>>  	}
>>
>> +	/*
>> +	 * Multichannel is not meaningful if max_channels is 1.
>> +	 * Force multichannel to false to ensure consistent configuration.
>> +	 */
>> +	if (ctx->multichannel && ctx->max_channels == 1)
>> +		ctx->multichannel = false;
>> +
>>  	return 0;
>>
>>   cifs_parse_mount_err:
>
>Do we even need ->multichannel flag at all? Maybe we could replace
>->multichannel for a function that checks for max_channels > 1?

I agree with Henrique.

I'd actually like to propose going even further and having the whole
module behaving as if multichannel was always on, even with
max_channels=1 -- the only difference being the need to run the
query_interfaces worker.

This is probably work for another patch/series though.


Cheers,

Enzo