Re: [PATCH 1/7] e2fsprogs: Add discard function into struct_io_manager

[Eric Sandeen <sandeen@redhat.com>]

On 11/16/10 2:16 PM, Lukas Czerner wrote:
> On Tue, 16 Nov 2010, Eric Sandeen wrote:
> 
>> On 10/26/10 12:54 PM, Lukas Czerner wrote:
>>> In order to provide generic "discard" function for all e2fsprogs tools
>>> add a discard function prototype into struct_io_manager. Specific
>>> function for specific io managers can be crated that way.
>>>
>>> This commit also creates unix_discard function which uses BLKDISCARD
>>> ioctl to discard data blocks on the block device and bind it into
>>> unit_io_manager structure to be available for all e2fsprogs tools.
>>> Note that BLKDISCARD is still Linux specific ioctl, however other
>>> unix systems may provide similar functionality. So far the
>>> unix_discard() remains linux specific hence is embedded in #ifdef
>>> __linux__ macro.
>>>
>>> Signed-off-by: Lukas Czerner <lczerner@redhat.com>
>>> ---
>>>  lib/ext2fs/ext2_io.h |    2 ++
>>>  lib/ext2fs/unix_io.c |   41 +++++++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 43 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/lib/ext2fs/ext2_io.h b/lib/ext2fs/ext2_io.h
>>> index ccc9c8b..d202007 100644
>>> --- a/lib/ext2fs/ext2_io.h
>>> +++ b/lib/ext2fs/ext2_io.h
>>> @@ -83,6 +83,8 @@ struct struct_io_manager {
>>>  					int count, void *data);
>>>  	errcode_t (*write_blk64)(io_channel channel, unsigned long long block,
>>>  					int count, const void *data);
>>> +	errcode_t (*discard)(io_channel channel, unsigned long long block,
>>> +			     unsigned long long count, const void *data);
>>>  	long	reserved[16];
>>>  };
>>>  
>>> diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
>>> index 1df1fdd..5b6cdec 100644
>>> --- a/lib/ext2fs/unix_io.c
>>> +++ b/lib/ext2fs/unix_io.c
>>> @@ -115,6 +115,8 @@ static errcode_t unix_read_blk64(io_channel channel, unsigned long long block,
>>>  			       int count, void *data);
>>>  static errcode_t unix_write_blk64(io_channel channel, unsigned long long block,
>>>  				int count, const void *data);
>>> +static errcode_t unix_discard(io_channel channel, unsigned long long block,
>>> +			      unsigned long long count, const void *data);
>>>  
>>>  static struct struct_io_manager struct_unix_manager = {
>>>  	EXT2_ET_MAGIC_IO_MANAGER,
>>> @@ -130,6 +132,7 @@ static struct struct_io_manager struct_unix_manager = {
>>>  	unix_get_stats,
>>>  	unix_read_blk64,
>>>  	unix_write_blk64,
>>> +	unix_discard,
>>>  };
>>>  
>>>  io_manager unix_io_manager = &struct_unix_manager;
>>> @@ -834,3 +837,41 @@ static errcode_t unix_set_option(io_channel channel, const char *option,
>>>  	}
>>>  	return EXT2_ET_INVALID_ARGUMENT;
>>>  }
>>> +
>>> +#ifdef __linux__
>>> +
>>> +#ifndef BLKDISCARD
>>> +#define BLKDISCARD	_IO(0x12,119)
>>> +#endif
>>> +
>>> +static errcode_t unix_discard(io_channel channel, unsigned long long block,
>>> +			     unsigned long long count, const void *data)
>>> +{
>>> +
>>> +	struct struct_ext2_filsys *fs;
>>> +	struct unix_private_data *u_priv;
>>> +	errcode_t	retval = 0;
>>> +	__uint64_t	range[2];
>>> +	int		blocksize;
>>> +
>>> +	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
>>> +	u_priv = (struct unix_private_data *) channel->private_data;
>>> +	EXT2_CHECK_MAGIC(u_priv, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);
>>> +
>>> +	fs = (struct struct_ext2_filsys *) data;
>>> +	if (!fs)
>>> +		return EXT2_ET_INVALID_ARGUMENT;
>>> +
>>> +	blocksize = EXT2_BLOCK_SIZE(fs->super);
>>
>> This seems a little convoluted; you pass in *data, which gets you the fs,
>> from which you get the super, from which you get the blocksize,
>> which is all that you ever actually use here:
>>
>>> +	range[0] = (__uint64_t)(block);
>>> +	range[1] = (__uint64_t)(count);
>>> +	range[0] *= (__uint64_t)(blocksize);
>>> +	range[1] *= (__uint64_t)(blocksize);
>>
>> any reason to not just pass in the blocksize?
>>
>> Maybe this is for flexibility for not-linux, but I guess we don't know what
>> they need anyway...?
>>
>> And if you do that you can change "u_priv" to "data" just to match the
>> other handlers, perhaps.
> 
> You're right, I was so closely following the example that I forget that
> it can be done more simply. Does this looks good to you ?
> 
> static errcode_t unix_discard(io_channel channel, unsigned long long block,
> 			     unsigned long long count, const void *blocksize)
> {
> 	unsigned int    *bsize = (unsigned int *) blocksize;

I think you can just pass in "int blocksize" right?

and 

ret = manager->discard(fs->io, start, count, fs->blocksize);

-Eric

> 	struct unix_private_data *data;
> 	errcode_t	retval = 0;
> 	__uint64_t	range[2];
> 
> 	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
> 	data = (struct unix_private_data *) channel->private_data;
> 	EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);
> 
> 	if (!blocksize)
> 		return EXT2_ET_INVALID_ARGUMENT;
> 
> 	range[0] = (__uint64_t)(block);
> 	range[1] = (__uint64_t)(count);
> 	range[0] *= (__uint64_t)(*bsize);
> 	range[1] *= (__uint64_t)(*bsize);
> 
> 	return ioctl(data->dev, BLKDISCARD, &range);
> }
> 
> then we can call it like this:
> 
> ret = manager->discard(fs->io, start, count, &fs->blocksize);
> 
> Thanks a lot for reviewing this!
> 
> -Lukas
> 
>>
>> -Eric
>>
>>> +	return ioctl(u_priv->dev, BLKDISCARD, &range);
>>> +}
>>> +
>>> +#else
>>> +#define unix_discard(channel, block, count)	EXT2_ET_UNIMPLEMENTED
>>> +#endif
>>
>>
>