Re: [PATCH] fs: create kiocb_{start,end}_write() helpers

[Amir Goldstein <amir73il@gmail.com>]

On Tue, Aug 15, 2023 at 8:06 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 8/15/23 11:02 AM, Jens Axboe wrote:
> > On 8/15/23 10:57 AM, Amir Goldstein wrote:
> >> +/**
> >> + * kiocb_start_write - get write access to a superblock for async file io
> >> + * @iocb: the io context we want to submit the write with
> >> + *
> >> + * This is a variant of file_start_write() for async io submission.
> >> + * Should be matched with a call to kiocb_end_write().
> >> + */
> >> +static inline void kiocb_start_write(struct kiocb *iocb)
> >> +{
> >> +    struct inode *inode = file_inode(iocb->ki_filp);
> >> +
> >> +    iocb->ki_flags |= IOCB_WRITE;
> >> +    if (WARN_ON_ONCE(iocb->ki_flags & IOCB_WRITE_STARTED))
> >> +            return;
> >> +    if (!S_ISREG(inode->i_mode))
> >> +            return;
> >> +    sb_start_write(inode->i_sb);
> >> +    /*
> >> +     * Fool lockdep by telling it the lock got released so that it
> >> +     * doesn't complain about the held lock when we return to userspace.
> >> +     */
> >> +    __sb_writers_release(inode->i_sb, SB_FREEZE_WRITE);
> >> +    iocb->ki_flags |= IOCB_WRITE_STARTED;
> >> +}
> >> +
> >> +/**
> >> + * kiocb_end_write - drop write access to a superblock after async file io
> >> + * @iocb: the io context we sumbitted the write with
> >> + *
> >> + * Should be matched with a call to kiocb_start_write().
> >> + */
> >> +static inline void kiocb_end_write(struct kiocb *iocb)
> >> +{
> >> +    struct inode *inode = file_inode(iocb->ki_filp);
> >> +
> >> +    if (!(iocb->ki_flags & IOCB_WRITE_STARTED))
> >> +            return;
> >> +    if (!S_ISREG(inode->i_mode))
> >> +            return;
>
> And how would IOCB_WRITE_STARTED ever be set, if S_ISREG() isn't true?

Good point.
I will pass is_reg argument from callers of kiocb_start_write() and
will only check IOCB_WRITE_STARTED in kiocb_end_write().

Thanks,
Amir.