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

[Konstantin Khorenko]

On 12/30/2020 08:32 AM, Vasily Averin wrote:
> 2 questions:
> 1) Is it used in our kernel?
Nope, not used, as it's said in the commit message.

> if not -- I afraid it will not be compiled
Will be.

> if so -- I doubt it should be exported.
Will be.

> By another words:
> are you sure "EXPORT_SYMBOL(generic_segment_checks);" line is required?
Yes, i'm sure.

i've tested zfs compilation on the test kernel without and with the patch.

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

Nope, it's not needed anymore.

We can probably drop PAGE_ITER - it's just a cleanup.
i'll send that patch once again.

> 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)
>>  {
>>
> .
>