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Re: [PATCH v3 2/5] fs: Add inode_update_time_writable

To: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Subject: Re: [PATCH v3 2/5] fs: Add inode_update_time_writable
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 20 Aug 2013 12:28:22 +1000
Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, Theodore Ts'o <tytso@xxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, Jan Kara <jack@xxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <a27accc2d9460b7ef194a203f305a18dafe926e8.1376679411.git.luto@xxxxxxxxxxxxxx>
References: <cover.1376679411.git.luto@xxxxxxxxxxxxxx> <a27accc2d9460b7ef194a203f305a18dafe926e8.1376679411.git.luto@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Fri, Aug 16, 2013 at 04:22:09PM -0700, Andy Lutomirski wrote:
> This is like file_update_time, except that it acts on a struct inode *
> instead of a struct file *.
> 
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> ---
>  fs/inode.c         | 72 
> ++++++++++++++++++++++++++++++++++++++++++------------
>  include/linux/fs.h |  1 +
>  2 files changed, 58 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index d6dfb09..bc90c12 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1637,6 +1637,34 @@ int file_remove_suid(struct file *file)
>  }
>  EXPORT_SYMBOL(file_remove_suid);
>  
> +/*
> + * This does the work that's common to file_update_time and
> + * inode_update_time.
> + */
> +static int prepare_update_cmtime(struct inode *inode, struct timespec *now)
> +{
> +     int sync_it;
> +
> +     /* First try to exhaust all avenues to not sync */
> +     if (IS_NOCMTIME(inode))
> +             return 0;
> +
> +     *now = current_fs_time(inode->i_sb);
> +     if (!timespec_equal(&inode->i_mtime, now))
> +             sync_it = S_MTIME;
> +
> +     if (!timespec_equal(&inode->i_ctime, now))
> +             sync_it |= S_CTIME;
> +
> +     if (IS_I_VERSION(inode))
> +             sync_it |= S_VERSION;
> +
> +     if (!sync_it)
> +             return 0;
> +
> +     return sync_it;
> +}
> +
>  /**
>   *   file_update_time        -       update mtime and ctime time
>   *   @file: file accessed
> @@ -1654,23 +1682,9 @@ int file_update_time(struct file *file)
>  {
>       struct inode *inode = file_inode(file);
>       struct timespec now;
> -     int sync_it = 0;
> +     int sync_it = prepare_update_cmtime(inode, &now);
>       int ret;
>  
> -     /* First try to exhaust all avenues to not sync */
> -     if (IS_NOCMTIME(inode))
> -             return 0;
> -
> -     now = current_fs_time(inode->i_sb);
> -     if (!timespec_equal(&inode->i_mtime, &now))
> -             sync_it = S_MTIME;
> -
> -     if (!timespec_equal(&inode->i_ctime, &now))
> -             sync_it |= S_CTIME;
> -
> -     if (IS_I_VERSION(inode))
> -             sync_it |= S_VERSION;
> -
>       if (!sync_it)
>               return 0;
>  
> @@ -1685,6 +1699,34 @@ int file_update_time(struct file *file)
>  }
>  EXPORT_SYMBOL(file_update_time);
>  
> +/**
> + *   inode_update_time_writable      -       update mtime and ctime time
> + *   @inode: inode accessed
> + *
> + *   This is like file_update_time, but it assumes the mnt is writable
> + *   and takes an inode parameter instead.  (We need to assume the mnt
> + *   was writable because inodes aren't associated with any particular
> + *   mnt.
> + */
> +
> +int inode_update_time_writable(struct inode *inode)
> +{
> +     struct timespec now;
> +     int sync_it = prepare_update_cmtime(inode, &now);
> +     int ret;
> +
> +     if (!sync_it)
> +             return 0;
> +
> +     /* sb_start_pagefault and update_time can both sleep. */
> +     sb_start_pagefault(inode->i_sb);
> +     ret = update_time(inode, &now, sync_it);
> +     sb_end_pagefault(inode->i_sb);

This gets called from the writeback path - you can't use
sb_start_pagefault/sb_end_pagefault in that path.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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