Re: [PATCH] vfs: Export fallocate facility to kernel modules

[Tyler Hicks <tyhicks@canonical.com>]

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On 2011-11-16 12:22:41, Thieu Le wrote:
> Export fallocate facility so layered file systems such as ecryptfs can
> take advantage of this feature.  One example of the need for fallocate
> is by ecryptfs.  ecryptfs has recently switched to a writeback cache
> model so its dirty pages are not written to the lower file system
> immediately.  In order to ensure that space is available when the page
> is later written, ecryptfs can efficiently preallocate that space using
> vfs_fallocate().
> 
> vfs_fallocate() does not perform all of the checkings of do_fallocate()
> because those checks are done higher in the stack.  Checking of offset and
> len are done by rw_verify_area() and generic_write_checks().  These
> functions are called by VFS before ecryptfs invokes vfs_fallocate() in its
> ecryptfs_write_end() function.  And since ecryptfs directly opens the lower
> file, it ensures that the file is opened with the proper flags and mode.

This looks good to me. Feel free to add my Reviewed-by. Of course, it
will need final sign-off by Al and/or Christoph.

Tyler

> 
> Signed-off-by: Thieu Le <thieule@chromium.org>
> ---
>  fs/open.c          |   32 ++++++++++++++++++++------------
>  include/linux/fs.h |    2 ++
>  2 files changed, 22 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/open.c b/fs/open.c
> index 22c41b5..65c0049 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -214,13 +214,9 @@ SYSCALL_ALIAS(sys_ftruncate64, SyS_ftruncate64);
>  #endif /* BITS_PER_LONG == 32 */
>  
>  
> -int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> +int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>  {
>  	struct inode *inode = file->f_path.dentry->d_inode;
> -	long ret;
> -
> -	if (offset < 0 || len <= 0)
> -		return -EINVAL;
>  
>  	/* Return error if mode is not supported */
>  	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
> @@ -231,13 +227,28 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>  	    !(mode & FALLOC_FL_KEEP_SIZE))
>  		return -EOPNOTSUPP;
>  
> -	if (!(file->f_mode & FMODE_WRITE))
> -		return -EBADF;
> -
>  	/* It's not possible punch hole on append only file */
>  	if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
>  		return -EPERM;
>  
> +	if (!file->f_op->fallocate)
> +		return -EOPNOTSUPP;
> +
> +	return file->f_op->fallocate(file, mode, offset, len);
> +}
> +EXPORT_SYMBOL(vfs_fallocate);
> +
> +int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> +{
> +	struct inode *inode = file->f_path.dentry->d_inode;
> +	long ret;
> +
> +	if (offset < 0 || len <= 0)
> +		return -EINVAL;
> +
> +	if (!(file->f_mode & FMODE_WRITE))
> +		return -EBADF;
> +
>  	if (IS_IMMUTABLE(inode))
>  		return -EPERM;
>  
> @@ -263,10 +274,7 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>  	if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
>  		return -EFBIG;
>  
> -	if (!file->f_op->fallocate)
> -		return -EOPNOTSUPP;
> -
> -	return file->f_op->fallocate(file, mode, offset, len);
> +	return vfs_fallocate(file, mode, offset, len);
>  }
>  
>  SYSCALL_DEFINE(fallocate)(int fd, int mode, loff_t offset, loff_t len)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 0c4df26..e7d26ee 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1524,6 +1524,8 @@ extern int vfs_link(struct dentry *, struct inode *, struct dentry *);
>  extern int vfs_rmdir(struct inode *, struct dentry *);
>  extern int vfs_unlink(struct inode *, struct dentry *);
>  extern int vfs_rename(struct inode *, struct dentry *, struct inode *, struct dentry *);
> +extern int vfs_fallocate(struct file *file, int mode, loff_t offset,
> +			 loff_t len);
>  
>  /*
>   * VFS dentry helper functions.
> -- 
> 1.7.3.1
> 
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