linux-kernel - Re: [PATCH bpf-next v5 3/5] bpf: Add bpf_fget

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Message-ID:
 <AM6PR03MB5080248C764D651CBB1FA301993D2@AM6PR03MB5080.eurprd03.prod.outlook.com>
Date: Tue, 10 Dec 2024 16:21:24 +0000
From: Juntong Deng <juntong.deng@...look.com>
To: Christian Brauner <brauner@...nel.org>
Cc: ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com,
 andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
 yonghong.song@...ux.dev, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, memxor@...il.com, snorcht@...il.com,
 bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 3/5] bpf: Add bpf_fget_task() kfunc

On 2024/12/10 14:28, Christian Brauner wrote:
> On Tue, Dec 10, 2024 at 02:03:52PM +0000, Juntong Deng wrote:
>> This patch adds bpf_fget_task() kfunc.
>>
>> bpf_fget_task() is used to get a pointer to the struct file
>> corresponding to the task file descriptor. Note that this function
>> acquires a reference to struct file.
>>
>> Signed-off-by: Juntong Deng <juntong.deng@...look.com>
>> ---
>>   fs/bpf_fs_kfuncs.c | 21 +++++++++++++++++++++
>>   1 file changed, 21 insertions(+)
>>
>> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
>> index 3fe9f59ef867..19a9d45c47f9 100644
>> --- a/fs/bpf_fs_kfuncs.c
>> +++ b/fs/bpf_fs_kfuncs.c
>> @@ -152,6 +152,26 @@ __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
>>   	return bpf_get_dentry_xattr(dentry, name__str, value_p);
>>   }
>>   
>> +/**
>> + * bpf_fget_task() - Get a pointer to the struct file corresponding to
>> + * the task file descriptor
>> + *
>> + * Note that this function acquires a reference to struct file.
>> + *
>> + * @task: the specified struct task_struct
>> + * @fd: the file descriptor
>> + *
>> + * @returns the corresponding struct file pointer if found,
>> + * otherwise returns NULL
>> + */
>> +__bpf_kfunc struct file *bpf_fget_task(struct task_struct *task, unsigned int fd)
>> +{
>> +	struct file *file;
>> +
>> +	file = fget_task(task, fd);
>> +	return file;
> 
> Why the local variable?

Thanks for your reply.

Uh, I forgot why I wrote it like that.

Yes, I agree that it is redundant.

I will remove it in the next version.