[Devel] [PATCH rh7] fs: Resurrect generic_segment_checks()

[Vasily Averin]

2 questions:
1) Is it used in our kernel?
if not -- I afraid it will not be compiled
if so -- I doubt it should be exported.
By another words:
are you sure "EXPORT_SYMBOL(generic_segment_checks);" line is required?

2) your previous patch-set "fs/iov_iter: Fix ZFS kernel module compilation" is still required too?

Thank you,
	Vasily Averin

On 12/29/20 4:40 PM, Konstantin Khorenko wrote:
> This is a partial revert of a9ca9d715754 ("kill generic_segment_checks()").
> 
> The patch resurrects the function, but does not restore any call for it.
> 
> Why this functiona is needed then?
> For zfs.
> 
> VZ kernel does not have file_operations::read_iter()/write_iter()
> compatible with mainstream version thus zfs external module
> tries live without iters and assumes generic_segment_checks() exists.
> 
> So keep the generic_segment_checks() specially for zfs.
> 
> https://bugs.openvz.org/browse/OVZ-7243
> 
> Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
> ---
>  include/linux/fs.h |  2 ++
>  mm/filemap.c       | 39 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 41 insertions(+)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 8398ec202a42..aee8adfc1252 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3255,6 +3255,8 @@ extern ssize_t generic_file_buffered_write_iter(struct kiocb *, struct iov_iter
>  		loff_t, loff_t *, ssize_t);
>  extern ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos);
>  extern ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos);
> +extern int generic_segment_checks(const struct iovec *iov,
> +		unsigned long *nr_segs, size_t *count, int access_flags);
>  
>  /* fs/block_dev.c */
>  extern ssize_t blkdev_aio_read(struct kiocb *, const struct iovec *,
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 950d92b6059b..585c57ef1e0a 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1981,6 +1981,45 @@ int file_read_actor(read_descriptor_t *desc, struct page *page,
>  	return size;
>  }
>  
> +/*
> + * Performs necessary checks before doing a write
> + * @iov:	io vector request
> + * @nr_segs:	number of segments in the iovec
> + * @count:	number of bytes to write
> + * @access_flags: type of access: %VERIFY_READ or %VERIFY_WRITE
> + *
> + * Adjust number of segments and amount of bytes to write (nr_segs should be
> + * properly initialized first). Returns appropriate error code that caller
> + * should return or zero in case that write should be allowed.
> + */
> +int generic_segment_checks(const struct iovec *iov,
> +			unsigned long *nr_segs, size_t *count, int access_flags)
> +{
> +	unsigned long   seg;
> +	size_t cnt = 0;
> +	for (seg = 0; seg < *nr_segs; seg++) {
> +		const struct iovec *iv = &iov[seg];
> +
> +		/*
> +		 * If any segment has a negative length, or the cumulative
> +		 * length ever wraps negative then return -EINVAL.
> +		 */
> +		cnt += iv->iov_len;
> +		if (unlikely((ssize_t)(cnt|iv->iov_len) < 0))
> +			return -EINVAL;
> +		if (access_ok(access_flags, iv->iov_base, iv->iov_len))
> +			continue;
> +		if (seg == 0)
> +			return -EFAULT;
> +		*nr_segs = seg;
> +		cnt -= iv->iov_len;	/* This segment is no good */
> +		break;
> +	}
> +	*count = cnt;
> +	return 0;
> +}
> +EXPORT_SYMBOL(generic_segment_checks);
> +
>  static int file_read_iter_actor(read_descriptor_t *desc, struct page *page,
>  				unsigned long offset, unsigned long size)
>  {
>