Re: Re: [PATCH 2/2] ceph: Implement writev/pwritev for sync operation.

[majianpeng <majianpeng@gmail.com>]

>Hi,
>
>Thank you for the patch.
>
>On 09/03/2013 04:52 PM, majianpeng wrote:
>> For writev/pwritev sync-operatoin, ceph only do the first iov.
>> It don't think other iovs.Now implement this.
>> I divided the write-sync-operation into two functions.One for
>> direct-write,other for none-direct-sync-write.This is because for
>> none-direct-sync-write we can merge iovs to one.But for direct-write,
>> we can't merge iovs.
>> 
>> Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
>> ---
>>  fs/ceph/file.c | 328 +++++++++++++++++++++++++++++++++++++++++++--------------
>>  1 file changed, 248 insertions(+), 80 deletions(-)
>> 
>> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
>> index 7d6a3ee..42c97b3 100644
>> --- a/fs/ceph/file.c
>> +++ b/fs/ceph/file.c
>> @@ -533,17 +533,19 @@ static void ceph_sync_write_unsafe(struct ceph_osd_request *req, bool unsafe)
>>  	}
>>  }
>>  
>> +
>>  /*
>> - * Synchronous write, straight from __user pointer or user pages (if
>> - * O_DIRECT).
>> + * Synchronous write, straight from __user pointer or user pages.
>>   *
>>   * If write spans object boundary, just do multiple writes.  (For a
>>   * correct atomic write, we should e.g. take write locks on all
>>   * objects, rollback on failure, etc.)
>>   */
>> -static ssize_t ceph_sync_write(struct file *file, const char __user *data,
>> -			       size_t left, loff_t pos, loff_t *ppos)
>> +static ssize_t
>> +ceph_sync_direct_write(struct kiocb *iocb, const struct iovec *iov,
>> +		       unsigned long nr_segs, size_t count)
>>  {
>> +	struct file *file = iocb->ki_filp;
>>  	struct inode *inode = file_inode(file);
>>  	struct ceph_inode_info *ci = ceph_inode(inode);
>>  	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
>> @@ -557,59 +559,55 @@ static ssize_t ceph_sync_write(struct file *file, const char __user *data,
>>  	int written = 0;
>>  	int flags;
>>  	int check_caps = 0;
>> -	int page_align, io_align;
>> -	unsigned long buf_align;
>> -	int ret;
>> +	int page_align;
>> +	int ret, i;
>>  	struct timespec mtime = CURRENT_TIME;
>> -	bool own_pages = false;
>> +	loff_t pos = iocb->ki_pos;
>>  
>>  	if (ceph_snap(file_inode(file)) != CEPH_NOSNAP)
>>  		return -EROFS;
>>  
>> -	dout("sync_write on file %p %lld~%u %s\n", file, pos,
>> -	     (unsigned)left, (file->f_flags & O_DIRECT) ? "O_DIRECT" : "");
>> +	dout("sync_direct_write on file %p %lld~%u\n", file, pos,
>> +	     (unsigned)count);
>>  
>> -	ret = filemap_write_and_wait_range(inode->i_mapping, pos, pos + left);
>> +	ret = filemap_write_and_wait_range(inode->i_mapping, pos, pos + count);
>>  	if (ret < 0)
>>  		return ret;
>>  
>>  	ret = invalidate_inode_pages2_range(inode->i_mapping,
>>  					    pos >> PAGE_CACHE_SHIFT,
>> -					    (pos + left) >> PAGE_CACHE_SHIFT);
>> +					    (pos + count) >> PAGE_CACHE_SHIFT);
>>  	if (ret < 0)
>>  		dout("invalidate_inode_pages2_range returned %d\n", ret);
>>  
>>  	flags = CEPH_OSD_FLAG_ORDERSNAP |
>>  		CEPH_OSD_FLAG_ONDISK |
>>  		CEPH_OSD_FLAG_WRITE;
>> -	if ((file->f_flags & (O_SYNC|O_DIRECT)) == 0)
>> -		flags |= CEPH_OSD_FLAG_ACK;
>> -	else
>> -		num_ops++;	/* Also include a 'startsync' command. */
>> +	num_ops++;	/* Also include a 'startsync' command. */
>>  
>> -	/*
>> -	 * we may need to do multiple writes here if we span an object
>> -	 * boundary.  this isn't atomic, unfortunately.  :(
>> -	 */
>> -more:
>> -	io_align = pos & ~PAGE_MASK;
>> -	buf_align = (unsigned long)data & ~PAGE_MASK;
>> -	len = left;
>> +	for (i = 0; i < nr_segs && count; i++) {
>
>POSIX requires that write syscall is atomic. I means we should allocate a single OSD request
>for all buffer segments that belong to the same object.
>
I think we could not.
For direct write, we use ceph_get_direct_page_vector to get pages.
Given iov1 and iov2 are in the same object. But we can't make the pages of iov1/2 to join together.
Because for ceph page_vector,it only record the offset of first page.

Or am i missing something?
Maybe we can use ceph pagelist but it will copy data.

Thanks!
Jianpeng Ma
>Regards
>Yan, Zheng