Re: [PATCH] f2fs: fix wrong bfree and bavail

[Andreas Dilger]

On Sep 5, 2017, at 3:06 PM, Jaegeuk Kim <jaegeuk@xxxxxxxxxx> wrote:
> 
> This patch fixes bavail and bfree finally.
> 
> long    f_bfree;    /* free blocks in fs */
> long    f_bavail;   /* free blocks avail to non-superuser */
> 
> So, bfree represents all the reserved blocks, while bavail does the space only
> visible to normal user.
> 
> Fix: 3e6d0b4d9c1c ("f2fs: fix incorrect f_bfree calculation in ->statfs")
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.8+
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> ---
> fs/f2fs/super.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 7e29db227910..17cca4cb93af 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -955,8 +955,8 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf)
> 	buf->f_bsize = sbi->blocksize;
> 
> 	buf->f_blocks = total_count - start_count;
> -	buf->f_bfree = user_block_count - valid_user_blocks(sbi) + ovp_count;
> -	buf->f_bavail = user_block_count - valid_user_blocks(sbi) -
> +	buf->f_bfree = user_block_count - valid_user_blocks(sbi);
> +	buf->f_bavail = user_block_count - valid_user_blocks(sbi) - ovp_count -
> 						sbi->reserved_blocks;

To keep the statfs data more consistent, you could use:

	buf->f_bavail = buf->f_bfree - ovp_count - sbi->reserved_blocks;

That avoids the extra subtraction, and avoids (minor) issues if these values
change while this syscall is running.

Cheers, Andreas

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