linux-kernel - Re: [PATCH 1/3] timerfd: convert to ->read

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Date: Thu, 4 Apr 2024 06:51:21 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org, brauner@...nel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] timerfd: convert to ->read_iter()

On 4/3/24 4:40 PM, Al Viro wrote:
> On Wed, Apr 03, 2024 at 08:02:52AM -0600, Jens Axboe wrote:
> 
>> -		res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
>> +		res = copy_to_iter(&ticks, sizeof(ticks), to);
> 
> Umm...  That's not an equivalent transformation - different behaviour on
> short copy; try to call it via read(fd, unmapped_buffer, 8) and see what
> happens.
> 
> copy_to_iter() returns the amount copied; no data copied => return 0, not -EFAULT.

Gah yes, ironically I did a bunch of conversions yesterday and it's all
fine. Not sure wha thappened here. I'll fix it up.

>> +	ufd = get_unused_fd_flags(O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
> 
> You do realize that get_unused_fd_flags() ignores O_RDWR (or
> O_NDELAY), right? Mixing those with O_CLOEXEC makes sense for
> anon_inode_getfd(), but here you have separate calls of
> get_unused_fd_flags() and anon_inode_getfile(), so...

I do, but figured it was cleaner that way. But I can change the flag
passing, ditto for the other ones.

-- 
Jens Axboe