linux-kernel - Re: [PATCH 4/7] VFS: Add generic_file_llseek

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Date:	Mon, 22 Aug 2011 18:08:34 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	viro@...iv.linux.org.uk, hch@...radead.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 4/7] VFS: Add generic_file_llseek_size

On 2011-08-22, at 2:49 PM, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> Add a generic_file_llseek variant to the VFS that allows passing in
> the current file size, instead of always using inode->i_size.
> This can be used to eliminate some cut'n'paste seek code in ext4.

I think your commit comment is incorrect.  It should read:

Add a generic_file_llseek_size() variant to the VFS that allows passing
in the maximum file size, instead of always using inode->i_sb->s_maxbytes.
This can be used to eliminate some cut'n'paste seek code in ext4.

Also, the function prototype in fs.h should take "loff_t maxbytes" instead
of "loff_t size".

> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
> fs/read_write.c    |   34 +++++++++++++++++++++++++++-------
> include/linux/fs.h |    2 ++
> 2 files changed, 29 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 8e8aab3..3d55cc6 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -51,14 +51,14 @@ static loff_t lseek_execute(struct file *file, struct inode *inode, loff_t offse
> }
> 
> /**
> - * generic_file_llseek - generic llseek implementation for regular files
> + * generic_file_llseek_size - generic llseek implementation for regular files
>  * @file:	file structure to seek on
>  * @offset:	file offset to seek to
>  * @origin:	type of seek
> + * @size:       max size of file system
>  *
> - * This is a generic implemenation of ->llseek useable for all normal local
> - * filesystems.  It just updates the file offset to the value specified by
> - * @offset and @origin under i_mutex.
> + * Variant of generic_file_llseek that allows passing in a custom
> + * file size.
>  *
>  * Synchronization:
>  * SEEK_SET is unsynchronized (but atomic on 64bit platforms)
> @@ -67,7 +67,8 @@ static loff_t lseek_execute(struct file *file, struct inode *inode, loff_t offse
>  * SEEK_END
>  */
> loff_t
> -generic_file_llseek(struct file *file, loff_t offset, int origin)
> +generic_file_llseek_size(struct file *file, loff_t offset, int origin, 
> +                         loff_t maxsize)
> {
> 	struct inode *inode = file->f_mapping->host;
> 
> @@ -91,7 +92,7 @@ generic_file_llseek(struct file *file, loff_t offset, int origin)
> 		 */
> 		spin_lock(&file->f_lock);
> 		offset = lseek_execute(file, inode, file->f_pos + offset, 
> -				       inode->i_sb->s_maxbytes);
> +				       maxsize);
> 		spin_unlock(&file->f_lock);
> 		return offset;
> 	case SEEK_DATA:
> @@ -113,7 +114,26 @@ generic_file_llseek(struct file *file, loff_t offset, int origin)
> 		break;
> 	}
> 
> -	return lseek_execute(file, inode, offset, inode->i_sb->s_maxbytes);
> +	return lseek_execute(file, inode, offset, maxsize);
> +}
> +EXPORT_SYMBOL(generic_file_llseek_size);
> +
> +/**
> + * generic_file_llseek - generic llseek implementation for regular files
> + * @file:	file structure to seek on
> + * @offset:	file offset to seek to
> + * @origin:	type of seek
> + *
> + * This is a generic implemenation of ->llseek useable for all normal local
> + * filesystems.  It just updates the file offset to the value specified by
> + * @offset and @origin under i_mutex.
> + */
> +loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
> +{
> +	struct inode *inode = file->f_mapping->host;
> +
> +	return generic_file_llseek_size(file, offset, origin, 
> +					inode->i_sb->s_maxbytes);
> }
> EXPORT_SYMBOL(generic_file_llseek);
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3417259..d64b601 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2395,6 +2395,8 @@ file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
> extern loff_t noop_llseek(struct file *file, loff_t offset, int origin);
> extern loff_t no_llseek(struct file *file, loff_t offset, int origin);
> extern loff_t generic_file_llseek(struct file *file, loff_t offset, int origin);
> +extern loff_t generic_file_llseek_size(struct file *file, loff_t offset, int origin,
> +				       loff_t size);
> extern int generic_file_open(struct inode * inode, struct file * filp);
> extern int nonseekable_open(struct inode * inode, struct file * filp);
> 
> -- 
> 1.7.4.4
> 
> --
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Cheers, Andreas





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