[RFC PATCH] fs: obtain the inode generation number from vfs directly

[Hongbo Li]

On 2024/8/27 10:13, Darrick J. Wong wrote:
> On Tue, Aug 27, 2024 at 01:41:08AM +0000, Hongbo Li wrote:
>> Many mainstream file systems already support the GETVERSION ioctl,
>> and their implementations are completely the same, essentially
>> just obtain the value of i_generation. We think this ioctl can be
>> implemented at the VFS layer, so the file systems do not need to
>> implement it individually.
> 
> What if a filesystem never touches i_generation?  Is it ok to advertise
> a generation number of zero when that's really meaningless?  Or should
> we gate the generic ioctl on (say) whether or not the fs implements file
> handles and/or supports nfs?

This ioctl mainly returns the i_generation, and whether it has meaning 
is up to the specific file system. Some tools will invoke 
IOC_GETVERSION, such as `lsattr -v`(but if it's lattr, it won't), but 
users may not necessarily actually use this value.

Thanks,
Hongbo

> 
> --D
> 
>> Signed-off-by: Hongbo Li <lihongbo22 at huawei.com>
>> ---
>>   fs/ioctl.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/fs/ioctl.c b/fs/ioctl.c
>> index 64776891120c..dff887ec52c4 100644
>> --- a/fs/ioctl.c
>> +++ b/fs/ioctl.c
>> @@ -878,6 +878,9 @@ static int do_vfs_ioctl(struct file *filp, unsigned int fd,
>>   	case FS_IOC_GETFSUUID:
>>   		return ioctl_getfsuuid(filp, argp);
>>   
>> +	case FS_IOC_GETVERSION:
>> +		return put_user(inode->i_generation, (int __user *)argp);
>> +
>>   	case FS_IOC_GETFSSYSFSPATH:
>>   		return ioctl_get_fs_sysfs_path(filp, argp);
>>   
>> @@ -992,6 +995,9 @@ COMPAT_SYSCALL_DEFINE3(ioctl, unsigned int, fd, unsigned int, cmd,
>>   		cmd = (cmd == FS_IOC32_GETFLAGS) ?
>>   			FS_IOC_GETFLAGS : FS_IOC_SETFLAGS;
>>   		fallthrough;
>> +	case FS_IOC32_GETVERSION:
>> +		cmd = FS_IOC_GETVERSION;
>> +		fallthrough;
>>   	/*
>>   	 * everything else in do_vfs_ioctl() takes either a compatible
>>   	 * pointer argument or no argument -- call it with a modified
>> -- 
>> 2.34.1
>>
>>
>