linux-kernel - Re: [PATCH 3/3] tmpfs: Initialize sysfs during tmpfs init

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Message-ID: <3754d3af-13bd-499b-9bca-633de721724f@igalia.com>
Date: Fri, 1 Nov 2024 13:23:55 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Hugh Dickins <hughd@...gle.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 krisman@...nel.org, Stephen Rothwell <sfr@...b.auug.org.au>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, kernel-dev@...lia.com,
 Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH 3/3] tmpfs: Initialize sysfs during tmpfs init

Em 01/11/2024 04:19, Nathan Chancellor escreveu:
> Hi André,
> 
> On Thu, Oct 31, 2024 at 10:37:41PM -0300, André Almeida wrote:
>> Instead of using fs_initcall(), initialize sysfs with the rest of the
>> filesystem. This is the right way to do it because otherwise any error
>> during tmpfs_sysfs_init() would get silently ignored. It's also useful
>> if tmpfs' sysfs ever need to display runtime information.
>>
>> Signed-off-by: André Almeida <andrealmeid@...lia.com>
>> ---
>>   mm/shmem.c | 130 ++++++++++++++++++++++++++++-------------------------
>>   1 file changed, 68 insertions(+), 62 deletions(-)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 6038e1d11987..8ff2f619f531 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -5126,6 +5126,66 @@ static struct file_system_type shmem_fs_type = {
>>   	.fs_flags	= FS_USERNS_MOUNT | FS_ALLOW_IDMAP | FS_MGTIME,
>>   };
>>   
>> +#if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)
> 
> This condition...
> 
>> +static int __init tmpfs_sysfs_init(void)
>> +{
>> +	int ret;
>> +
>> +	tmpfs_kobj = kobject_create_and_add("tmpfs", fs_kobj);
>> +	if (!tmpfs_kobj)
>> +		return -ENOMEM;
>> +
>> +	ret = sysfs_create_group(tmpfs_kobj, &tmpfs_attribute_group);
>> +	if (ret)
>> +		kobject_put(tmpfs_kobj);
>> +
>> +	return ret;
>> +}
>> +#endif /* CONFIG_SYSFS && CONFIG_TMPFS */
>> +
>>   void __init shmem_init(void)
>>   {
>>   	int error;
>> @@ -5149,6 +5209,14 @@ void __init shmem_init(void)
>>   		goto out1;
>>   	}
>>   
>> +#ifdef CONFIG_SYSFS
> 
> and this condition are not the same, so there will be a compile error if
> CONFIG_SHMEM and CONFIG_SYSFS are enabled but CONFIG_TMPFS is not, such
> as with ARCH=x86_64 allnoconfig for me:
> 
>    mm/shmem.c: In function 'shmem_init':
>    mm/shmem.c:5243:17: error: implicit declaration of function 'tmpfs_sysfs_init'; did you mean 'uids_sysfs_init'? [-Wimplicit-function-declaration]
>     5243 |         error = tmpfs_sysfs_init();
>          |                 ^~~~~~~~~~~~~~~~
>          |                 uids_sysfs_init
> 

Thanks for the catch! Fixed for v2

>> +	error = tmpfs_sysfs_init();
>> +	if (error) {
>> +		pr_err("Could not init tmpfs sysfs\n");
>> +		goto out1;
>> +	}
>> +#endif
> 
> Cheers,
> Nathan