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Re: [PATCH v7 1/11] fs: Add support FALLOC_FL_INSERT_RANGE for fallocate

To: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
Subject: Re: [PATCH v7 1/11] fs: Add support FALLOC_FL_INSERT_RANGE for fallocate
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Tue, 6 Jan 2015 11:32:20 -0500
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, "Theodore Ts'o" <tytso@xxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ext4 <linux-ext4@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, Ashish Sangwan <a.sangwan@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <003f01d02670$27a5e300$76f1a900$@samsung.com>
References: <003f01d02670$27a5e300$76f1a900$@samsung.com>
User-agent: Mutt/1.5.23 (2014-03-12)
On Fri, Jan 02, 2015 at 06:40:33PM +0900, Namjae Jeon wrote:
> FALLOC_FL_INSERT_RANGE command is the opposite command of
> FALLOC_FL_COLLAPSE_RANGE that is needed for advertisers or someone who want to
> add some data in the middle of file. FALLOC_FL_INSERT_RANGE will create space
> for writing new data within a file after shifting extents to right as given
> length. and this command also has same limitation as FALLOC_FL_COLLAPSE_RANGE,
> that is block boundary and use ftruncate(2) for crosses EOF.
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
> Signed-off-by: Ashish Sangwan <a.sangwan@xxxxxxxxxxx>
> ---
>  fs/open.c                   |  8 +++++++-
>  include/uapi/linux/falloc.h | 15 +++++++++++++++
>  2 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/open.c b/fs/open.c
> index 36662d0..74ed498 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -232,7 +232,8 @@ int do_fallocate(struct file *file, int mode, loff_t 
> offset, loff_t len)
>  
>       /* Return error if mode is not supported */
>       if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
> -                  FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE))
> +                  FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |
> +                  FALLOC_FL_INSERT_RANGE))
>               return -EOPNOTSUPP;
>  
>       /* Punch hole and zero range are mutually exclusive */
> @@ -250,6 +251,11 @@ int do_fallocate(struct file *file, int mode, loff_t 
> offset, loff_t len)
>           (mode & ~FALLOC_FL_COLLAPSE_RANGE))
>               return -EINVAL;
>  
> +     /* Insert range should only be used exclusively. */
> +     if ((mode & FALLOC_FL_INSERT_RANGE) &&
> +         (mode & ~FALLOC_FL_INSERT_RANGE))
> +             return -EINVAL;
> +
>       if (!(file->f_mode & FMODE_WRITE))
>               return -EBADF;
>  
> diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
> index d1197ae..1f20723 100644
> --- a/include/uapi/linux/falloc.h
> +++ b/include/uapi/linux/falloc.h
> @@ -41,4 +41,19 @@
>   */
>  #define FALLOC_FL_ZERO_RANGE         0x10
>  
> +/*
> + * FALLOC_FL_INSERT_RANGE is use to insert space within the file size without

                                used

> + * overwriting any existing data. The contents of the file beyond offset are
> + * shifted towards right by len bytes to create a hole.  As such, this
> + * operation will increase the size of the file by len bytes.

I suppose we should split this comment up into a few paragraphs similar
to the collapse range comment it is based on. That means we split
here...

> + * Different filesystems may implement different limitations on the 
> granularity
> + * of the operation. Most will limit operations to filesystem block size
> + * boundaries, but this boundary may be larger or smaller depending on
> + * the filesystem and/or the configuration of the filesystem or file.

... and here.

Otherwise this looks fine to me.

Brian

> + * Attempting to insert space using this flag at OR beyond the end of
> + * the file is considered an illegal operation - just use ftruncate(2) or
> + * fallocate(2) with mode 0 for such type of operations.
> + */
> +#define FALLOC_FL_INSERT_RANGE               0x20
> +
>  #endif /* _UAPI_FALLOC_H_ */
> -- 
> 1.7.11-rc0
> 

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