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Message-Id: <03D226D6-9598-473F-90FC-03A389E2A625@dilger.ca>
Date: Sun, 23 Jun 2013 11:00:51 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: Namjae Jeon <linkinjeon@...il.com>
Cc: "tytso@....edu" <tytso@....edu>,
"adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
"a.sangwan@...sung.com" <a.sangwan@...sung.com>,
Namjae Jeon <linkinjeon@...il.com>,
Namjae Jeon <namjae.jeon@...sung.com>
Subject: Re: [PATCH 0/3] ext4: introduce two new ioctls
On 2013-06-23, at 0:07, Namjae Jeon <linkinjeon@...il.com> wrote:
> From: Namjae Jeon <namjae.jeon@...sung.com>
>
> This patch series introduces 2 new ioctls for ext4.
>
> Truncate_block_range ioctl truncates blocks from source file.
How is this different from fallocate(FALLOC_FL_PUNCH_HOLE)? That is already in existing kernels, and portable across multiple filesystems.
> Transfer_block_range ioctl transfers data blocks from source file
> and append them at the end of destination file.
There is already a similar ioctl for defragmenting files. Is it possible to use that, or does it have different semantics?
> Ioctl1: EXT4_IOC_TRUNCATE_BLOCK_RANGE:
> This ioctl truncates a range of data blocks from file.
> It is useful to remove easily and quickly the garbage data
> at the middle of file.
>
> e.g. we have a movie file and there is long advertisement in movie file.
> user want to remove only advertisement range.
While this works in theory, there is very little chance that the movie data will align exactly to filesystem block boundaries.
Cheers, Andreas
> 1) Movie file (8GB), There is the adverisement of 500MB size.
> ____________________________________________________________________
> | | | |
> | a) range | b) Advertisement | c) range |
> | | (unneeded data) | |
> |_____________________|___________________|_________________________|
>
> 2) Currently if user want to remove portion b), the conventional way
> would be to copy a) and c) (7.5GB) to new file by reading data from
> original file and writing to new file, followed up by delete original
> file and rename new file. It will take long time.
> When we measure time, it takes around 3 minutes.
>
> 3) If we use EXT4_IOC_TRUNCATE_BLOCK_RANGE, we can have garbage data removed
> in less than a second. Also, no need to perform deletion and rename.
> _______________________________________________
> | | |
> | a) range | c) range |
> | | |
> |_____________________|________________________|
>
>
> #define EXT4_IOC_TRUNCATE_BLOCK_RANGE _IOW('f', 18, struct truncate_range)
> struct truncate_range {
> __u32 start_block;
> __u32 length;
> };
>
> example =>
> Originally the file "abc" has the below extent tree:
> debugfs: ex abc
> Level Entries Logical Physical Length Flags
> 0/ 0 1/ 3 0 - 4 33615 - 33619 5
> 0/ 0 2/ 3 5 - 9 33855 - 33859 5
> 0/ 0 3/ 3 10 - 14 69657 - 69661 5
>
> ls -lh abc
> -rw-r--r-- 1 root 0 60.0K Jan 1 00:01 abc
>
> du -h abc
> 60.0K abc
>
> e4_truncate_block_range abc 2 10
> Return:
> : Success
>
> After executing truncate_block_range ioctl, the extent tree:
> ex abc
> Level Entries Logical Physical Length Flags
> 0/ 0 1/ 2 0 - 1 33615 - 33616 2
> 0/ 0 2/ 2 2 - 4 69659 - 69661 3
>
> ls -lh abc
> -rw-r--r-- 1 root 0 20.0K Jan 1 00:08 abc
>
> du -h abc
> 20.0K abc
>
> This ioctl works in 2 parts:
> 1) remove _only_ data blocks that resides within specified range.
> If the entire range is a hole than nothing is removed.
>
> 2) update file's logical block offsets ranging from block number
> "start_block + length" to last logical block of file such that
> lblk_number = lblk_number - length;
> This is done by updating starting block of all the extents that
> resides within the range.
>
> If "start_block + length" is already equal to the last block of file
> than no block is updated. This case is similar to convential truncate.
>
> In the above example:
> The data blocks ranging from [2 - 11] have been removed
> and the logical offsets of the file beyond block number 12 till last block
> of file are updated by subtracting length from each of logical numbers.
> This gives a contiguous logical space to the file.
> Also, the logical size and disksize of the file are updated accordingly.
>
> Ioctl2: EXT4_IOC_TRANSFER_BLOCK_RANGE:
> This ioctl transfers a range of data blocks from source file and append
> them at the end of the destination file.
> This is not actual data transfer but only metadata is moved.
>
> ____________________________________________________________________
> | | | |
> | a) range | b) range | c) range |
> | | | |
> |_____________________|___________________|_________________________|
>
> If user does not want b) in the orig file but wants to make a new file
> comprising only b) OR wants b) at the end of an already existing file,
> the conventional way of doing it would be to:
> 1) Copy b) to new file
> 2) Copy c) to temp file
> 3) Truncate orig file to a)
> 4) Copy c) from temp file to the end of orig file.
> 5) Delete temp file.
>
> After this operations =>
> orig_file:
> __________________________________________
> | | |
> | a) range | c) range |
> | | |
> |_____________________|___________________|
>
> new_file:
> _______________________
> | |
> | b) range |
> | |
> |_____________________|
>
> Again, this operation would take a long time (depending on the sizes of range)
> if done using conventional way while using transfer_block_range ioctl reduces
> the time within a second.
>
> #define EXT4_IOC_TRANSFER_BLOCK_RANGE _IOW('f', 19, struct transfer_range)
> struct transfer_range {
> __u32 dest_fd;
> __u32 start_block;
> __u32 length;
> };
>
> example=>
> debugfs: ex source
> Level Entries Logical Physical Length Flags
> 0/ 1 1/ 1 0 - 24 32809 25
> 1/ 1 1/ 5 0 - 4 4071 - 4075 5
> 1/ 1 2/ 5 5 - 9 4081 - 4085 5
> 1/ 1 3/ 5 10 - 14 4091 - 4095 5
> 1/ 1 4/ 5 15 - 19 4101 - 4105 5
> 1/ 1 5/ 5 20 - 24 4151 - 4155 5
>
> debugfs: ex dest
> Level Entries Logical Physical Length Flags
> 0/ 0 1/ 3 0 - 4 32825 - 32829 5
> 0/ 0 2/ 3 5 - 9 33545 - 33549 5
> 0/ 0 3/ 3 10 - 14 33615 - 33619 5
>
> ls -lh source
> -rw-r--r-- 1 root 0 100.0K Jan 1 00:01 source
> ls -lh dest
> -rw-r--r-- 1 root 0 60.0K Jan 1 00:01 dest
>
> du -h source
> 104.0K source
> du -h dest
> 60.0K dest
>
> e4_transfer_block_range source dest 2 10
> Return:
> : Success
>
> debugfs: ex source
> Level Entries Logical Physical Length Flags
> 0/ 1 1/ 1 0 - 24 32809 25
> 1/ 1 1/ 4 0 - 1 4071 - 4072 2
> 1/ 1 2/ 4 12 - 14 4093 - 4095 3
> 1/ 1 3/ 4 15 - 19 4101 - 4105 5
> 1/ 1 4/ 4 20 - 24 4151 - 4155 5
> debugfs: ex dest
> Level Entries Logical Physical Length Flags
> 0/ 1 1/ 1 0 - 24 32835 25
> 1/ 1 1/ 6 0 - 4 32825 - 32829 5
> 1/ 1 2/ 6 5 - 9 33545 - 33549 5
> 1/ 1 3/ 6 10 - 14 33615 - 33619 5
> 1/ 1 4/ 6 15 - 17 4073 - 4075 3
> 1/ 1 5/ 6 18 - 22 4081 - 4085 5
> 1/ 1 6/ 6 23 - 24 4091 - 4092 2
>
> ls -lh source
> -rw-r--r-- 1 root 0 100.0K Jan 1 00:04 source
> ls -lh dest
> -rw-r--r-- 1 root 0 100.0K Jan 1 00:04 dest
>
> du -h source
> 64.0K source
> du -h dest
> 104.0K dest
>
> The data blocks lying between [start_block to start_block + length) are appended
> contiguously at the end of destination file.
> The block transfer leaves a hole in the source file.
> If any hole is encountered in the range, it is ommited.
>
> This ioctl does not change the logical size of the source file hence
> leaves a hole in place of transfered range.
> If user want contiguous logical space for source file,
> it can truncate the hole by calling truncate_range_ioctl for source file.
>
> Example for above "source" file:
> e4_truncate_block_range source 2 10
> Return:
> : Success
> debugfs: ex source
> Level Entries Logical Physical Length Flags
> 0/ 1 1/ 1 0 - 14 32809 15
> 1/ 1 1/ 4 0 - 1 4071 - 4072 2
> 1/ 1 2/ 4 2 - 4 4093 - 4095 3
> 1/ 1 3/ 4 5 - 9 4101 - 4105 5
> 1/ 1 4/ 4 10 - 14 4151 - 4155 5
>
> Namjae Jeon (3):
> ext4: Add EXT4_IOC_TRUNCATE_BLOCK_RANGE ioctl
> ext4: make mext_next_extent non static and move get_ext_path
> ext4: Add EXT4_IOC_TRANSFER_BLOCK_RANGE ioctl
>
> --
> 1.7.9.5
>
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