linux-kernel - Re: [PATCH] Export shmem_file_setup and shmem

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Date:	Fri, 1 Aug 2008 11:57:44 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Eric Anholt <eric@...olt.net>
cc:	linux-kernel@...r.kernel.org, keithp@...thp.com
Subject: Re: [PATCH] Export shmem_file_setup and shmem_getpage for DRM-GEM

On Thu, 31 Jul 2008, Eric Anholt wrote:
> From: Keith Packard <keithp@...thp.com>
> 
> GEM needs to create shmem files and get pages related to a shmem file, and
> using this pair of functions is the easiest way to do that.

It's fine to be getting the GEM end working using this easiest way,
and I don't think we'll have a problem with EXPORT_SYMBOL_GPL() on
shmem_file_setup() or something very like it - it just happens that
its current callers are not in loadable modules.

But shmem_getpage() is very much an internal helper function for
mm/shmem.c, and I'm pretty sure we should keep it and its sgp_types
that way: I'll take a look at how you're using it later on, and see
what makes sense to offer instead.

And I don't think you should assume that all GEM users must have
CONFIG_SHMEM=y: we should aim for an interface that mm/tiny_shmem.c
(redirecting to ramfs) can also support.  I can believe that GEM and
TINY won't have much intersection, but let's not force that by using
shmem_getpage().

Hugh

> 
> Signed-off-by: Eric Anholt <eric@...olt.net>
> ---
>  include/linux/mm.h |   11 +++++++++++
>  mm/shmem.c         |   17 ++++-------------
>  2 files changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 866a3db..6e54210 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -715,6 +715,17 @@ static inline int shmem_lock(struct file *file, int lock,
>  #endif
>  struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags);
>  
> +/* Flag allocation requirements to shmem_getpage and shmem_swp_alloc */
> +enum sgp_type {
> +	SGP_READ,	/* don't exceed i_size, don't allocate page */
> +	SGP_CACHE,	/* don't exceed i_size, may allocate page */
> +	SGP_DIRTY,	/* like SGP_CACHE, but set new page dirty */
> +	SGP_WRITE,	/* may exceed i_size, may allocate page */
> +};
> +
> +int shmem_getpage(struct inode *inode, unsigned long idx,
> +		  struct page **pagep, enum sgp_type sgp, int *type);
> +
>  int shmem_zero_setup(struct vm_area_struct *);
>  
>  #ifndef CONFIG_MMU
> diff --git a/mm/shmem.c b/mm/shmem.c
> index c1e5a3b..7166ff3 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -77,14 +77,6 @@
>  /* Pretend that each entry is of this size in directory's i_size */
>  #define BOGO_DIRENT_SIZE 20
>  
> -/* Flag allocation requirements to shmem_getpage and shmem_swp_alloc */
> -enum sgp_type {
> -	SGP_READ,	/* don't exceed i_size, don't allocate page */
> -	SGP_CACHE,	/* don't exceed i_size, may allocate page */
> -	SGP_DIRTY,	/* like SGP_CACHE, but set new page dirty */
> -	SGP_WRITE,	/* may exceed i_size, may allocate page */
> -};
> -
>  #ifdef CONFIG_TMPFS
>  static unsigned long shmem_default_max_blocks(void)
>  {
> @@ -97,9 +89,6 @@ static unsigned long shmem_default_max_inodes(void)
>  }
>  #endif
>  
> -static int shmem_getpage(struct inode *inode, unsigned long idx,
> -			 struct page **pagep, enum sgp_type sgp, int *type);
> -
>  static inline struct page *shmem_dir_alloc(gfp_t gfp_mask)
>  {
>  	/*
> @@ -1177,8 +1166,8 @@ static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
>   * vm. If we swap it in we mark it dirty since we also free the swap
>   * entry since a page cannot live in both the swap and page cache
>   */
> -static int shmem_getpage(struct inode *inode, unsigned long idx,
> -			struct page **pagep, enum sgp_type sgp, int *type)
> +int shmem_getpage(struct inode *inode, unsigned long idx,
> +		  struct page **pagep, enum sgp_type sgp, int *type)
>  {
>  	struct address_space *mapping = inode->i_mapping;
>  	struct shmem_inode_info *info = SHMEM_I(inode);
> @@ -1431,6 +1420,7 @@ failed:
>  	}
>  	return error;
>  }
> +EXPORT_SYMBOL(shmem_getpage);
>  
>  static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
> @@ -2582,6 +2572,7 @@ put_memory:
>  	shmem_unacct_size(flags, size);
>  	return ERR_PTR(error);
>  }
> +EXPORT_SYMBOL(shmem_file_setup);
>  
>  /**
>   * shmem_zero_setup - setup a shared anonymous mapping
> -- 
> 1.5.6.3
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