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Date:	Thu, 2 Dec 2010 09:34:31 +0100 (CET)
From:	Lukas Czerner <lczerner@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>
cc:	Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [1/6] e2fsprogs: Add discard function into struct_io_manager

On Tue, 23 Nov 2010, Ted Ts'o wrote:

> On Thu, Nov 18, 2010 at 03:38:36AM -0000, 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@...hat.com>
> 
> I had to make a few cleanup changes before I could merge this into the
> master branch.
> 
> 1) unix_discard() was defined as a macro in the !__linux__ case.
> Since unix_discard() gets used to fill in a function pointer in the
> io_channel_ops structure, this would have caused non-linux compiles to
> break.
> 
> 2) I added a io_channel_discard() function which checks to see if
> io_channel->discard is non-NULL before dereferencing the function
> pointer (you had mke2fs and e2fsck blindly dereferencing the function
> pointer before checking to see if it was non-NULL; this is bad,
> because not all io_managers, in particular, not the test_io manager in
> your patches, support discard).
> 
> 3) I added support for discard to the test_io manager, which makes
> debugging much easier (just compile with --enable-testio-debug, and
> then set the TEST_IO_FLAGS environment variable).
> 
> 4) There was no need to pass the block size to the discard function.
> The blocksize is part of the io_channel abstraction, and is stored in
> the channel structure.
> 
> 					- Ted

Hi Ted,

sorry for the delay. Thanks a lot for your review, fixes and merge, it
looks good.

Thanks!

-Lukas

> 
> The resulting patch looked like this.
> 
> commit e90a59ed434d6c5e38dd148aa4ba5b22b8f7eb24
> Author: Lukas Czerner <lczerner@...hat.com>
> Date:   Thu Nov 18 03:38:36 2010 +0000
> 
>     e2fsprogs: Add discard function into struct_io_manager
>     
>     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@...hat.com>
>     Signed-off-by: Theodore Ts'o <tytso@....edu>
> 
> diff --git a/lib/ext2fs/ext2_io.h b/lib/ext2fs/ext2_io.h
> index ccc9c8b..f26b569 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);
>  	long	reserved[16];
>  };
>  
> diff --git a/lib/ext2fs/io_manager.c b/lib/ext2fs/io_manager.c
> index 6d0e234..80f9dfc 100644
> --- a/lib/ext2fs/io_manager.c
> +++ b/lib/ext2fs/io_manager.c
> @@ -99,3 +99,14 @@ errcode_t io_channel_write_blk64(io_channel channel, unsigned long long block,
>  	return (channel->manager->write_blk)(channel, (unsigned long) block,
>  					     count, data);
>  }
> +
> +errcode_t io_channel_discard(io_channel channel, unsigned long long block,
> +			     unsigned long long count)
> +{
> +	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
> +
> +	if (channel->manager->discard)
> +		return (channel->manager->discard)(channel, block, count);
> +
> +	return EXT2_ET_UNIMPLEMENTED;
> +}
> diff --git a/lib/ext2fs/test_io.c b/lib/ext2fs/test_io.c
> index 8d887a8..242d442 100644
> --- a/lib/ext2fs/test_io.c
> +++ b/lib/ext2fs/test_io.c
> @@ -73,7 +73,8 @@ static errcode_t test_write_byte(io_channel channel, unsigned long offset,
>  static errcode_t test_set_option(io_channel channel, const char *option,
>  				 const char *arg);
>  static errcode_t test_get_stats(io_channel channel, io_stats *stats);
> -
> +static errcode_t test_discard(io_channel channel, unsigned long long block,
> +			      unsigned long long count);
>  
>  static struct struct_io_manager struct_test_manager = {
>  	EXT2_ET_MAGIC_IO_MANAGER,
> @@ -89,6 +90,7 @@ static struct struct_io_manager struct_test_manager = {
>  	test_get_stats,
>  	test_read_blk64,
>  	test_write_blk64,
> +	test_discard,
>  };
>  
>  io_manager test_io_manager = &struct_test_manager;
> @@ -120,6 +122,7 @@ void (*test_io_cb_write_byte)
>  #define TEST_FLAG_FLUSH			0x08
>  #define TEST_FLAG_DUMP			0x10
>  #define TEST_FLAG_SET_OPTION		0x20
> +#define TEST_FLAG_DISCARD		0x40
>  
>  static void test_dump_block(io_channel channel,
>  			    struct test_private_data *data,
> @@ -495,3 +498,21 @@ static errcode_t test_get_stats(io_channel channel, io_stats *stats)
>  	}
>  	return retval;
>  }
> +
> +static errcode_t test_discard(io_channel channel, unsigned long long block,
> +			      unsigned long long count)
> +{
> +	struct test_private_data *data;
> +	errcode_t	retval = 0;
> +
> +	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
> +	data = (struct test_private_data *) channel->private_data;
> +	EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_TEST_IO_CHANNEL);
> +
> +	retval = io_channel_discard(channel, block, count);
> +	if (data->flags & TEST_FLAG_DISCARD)
> +		fprintf(data->outfile,
> +			"Test_io: discard(%llu, %llu) returned %s\n",
> +			block, count, retval ? error_message(retval) : "OK");
> +	return retval;
> +}
> diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
> index 1df1fdd..2302374 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);
>  
>  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 +837,31 @@ static errcode_t unix_set_option(io_channel channel, const char *option,
>  	}
>  	return EXT2_ET_INVALID_ARGUMENT;
>  }
> +
> +#if defined(__linux__) && !defined(BLKDISCARD)
> +#define BLKDISCARD	_IO(0x12,119)
> +#endif
> +
> +static errcode_t unix_discard(io_channel channel, unsigned long long block,
> +			      unsigned long long count)
> +{
> +#ifdef BLKDISCARD
> +	struct unix_private_data *data;
> +	__uint64_t	range[2];
> +	int		ret;
> +
> +	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);
> +
> +	range[0] = (__uint64_t)(block) * channel->block_size;
> +	range[1] = (__uint64_t)(count) * channel->block_size;
> +
> +	ret = ioctl(data->dev, BLKDISCARD, &range);
> +	if (ret < 0)
> +		return errno;
> +	return 0;
> +#else
> +	return EXT2_ET_UNIMPLEMENTED;
> +#endif
> +}
> 

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