RE: [PATCH v5 5/7] fsdax: Dedup file range to use a compare function

[ruansy.fnst@xxxxxxxxxxx]

> -----Original Message-----
> From: Darrick J. Wong <djwong@xxxxxxxxxx>
> Subject: Re: [PATCH v5 5/7] fsdax: Dedup file range to use a compare function
> 
> On Tue, May 11, 2021 at 11:09:31AM +0800, Shiyang Ruan wrote:
> > With dax we cannot deal with readpage() etc. So, we create a dax
> > comparison funciton which is similar with
> > vfs_dedupe_file_range_compare().
> > And introduce dax_remap_file_range_prep() for filesystem use.
> >
> > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> > Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> > ---
> >  fs/dax.c             | 56
> +++++++++++++++++++++++++++++++++++++++++++
> >  fs/remap_range.c     | 57
> +++++++++++++++++++++++++++++++++++++-------
> >  fs/xfs/xfs_reflink.c |  8 +++++--
> >  include/linux/dax.h  |  4 ++++
> >  include/linux/fs.h   | 12 ++++++----
> >  5 files changed, 123 insertions(+), 14 deletions(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index ee9d28a79bfb..dedf1be0155c 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -1853,3 +1853,59 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault
> *vmf,
> >  	return dax_insert_pfn_mkwrite(vmf, pfn, order);  }
> > EXPORT_SYMBOL_GPL(dax_finish_sync_fault);
> > +
> > +static loff_t dax_range_compare_actor(struct inode *ino1, loff_t pos1,
> > +		struct inode *ino2, loff_t pos2, loff_t len, void *data,
> > +		struct iomap *smap, struct iomap *dmap) {
> > +	void *saddr, *daddr;
> > +	bool *same = data;
> > +	int ret;
> > +
> > +	if (smap->type == IOMAP_HOLE && dmap->type == IOMAP_HOLE) {
> > +		*same = true;
> > +		return len;
> > +	}
> > +
> > +	if (smap->type == IOMAP_HOLE || dmap->type == IOMAP_HOLE) {
> > +		*same = false;
> > +		return 0;
> > +	}
> > +
> > +	ret = dax_iomap_direct_access(smap, pos1, ALIGN(pos1 + len, PAGE_SIZE),
> > +				      &saddr, NULL);
> > +	if (ret < 0)
> > +		return -EIO;
> > +
> > +	ret = dax_iomap_direct_access(dmap, pos2, ALIGN(pos2 + len, PAGE_SIZE),
> > +				      &daddr, NULL);
> > +	if (ret < 0)
> > +		return -EIO;
> > +
> > +	*same = !memcmp(saddr, daddr, len);
> > +	return len;
> > +}
> > +
> > +int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
> > +		struct inode *dest, loff_t destoff, loff_t len, bool *is_same,
> > +		const struct iomap_ops *ops)
> > +{
> > +	int id, ret = 0;
> > +
> > +	id = dax_read_lock();
> > +	while (len) {
> > +		ret = iomap_apply2(src, srcoff, dest, destoff, len, 0, ops,
> > +				   is_same, dax_range_compare_actor);
> > +		if (ret < 0 || !*is_same)
> > +			goto out;
> > +
> > +		len -= ret;
> > +		srcoff += ret;
> > +		destoff += ret;
> > +	}
> > +	ret = 0;
> > +out:
> > +	dax_read_unlock(id);
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(dax_dedupe_file_range_compare);
> > diff --git a/fs/remap_range.c b/fs/remap_range.c index
> > e4a5fdd7ad7b..7bc4c8e3aa9f 100644
> > --- a/fs/remap_range.c
> > +++ b/fs/remap_range.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/compat.h>
> >  #include <linux/mount.h>
> >  #include <linux/fs.h>
> > +#include <linux/dax.h>
> >  #include "internal.h"
> >
> >  #include <linux/uaccess.h>
> > @@ -199,9 +200,9 @@ static void vfs_unlock_two_pages(struct page *page1,
> struct page *page2)
> >   * Compare extents of two files to see if they are the same.
> >   * Caller must have locked both inodes to prevent write races.
> >   */
> > -static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
> > -					 struct inode *dest, loff_t destoff,
> > -					 loff_t len, bool *is_same)
> > +int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
> > +				  struct inode *dest, loff_t destoff,
> > +				  loff_t len, bool *is_same)
> >  {
> >  	loff_t src_poff;
> >  	loff_t dest_poff;
> > @@ -280,6 +281,7 @@ static int vfs_dedupe_file_range_compare(struct
> > inode *src, loff_t srcoff,
> >  out_error:
> >  	return error;
> >  }
> > +EXPORT_SYMBOL(vfs_dedupe_file_range_compare);
> >
> >  /*
> >   * Check that the two inodes are eligible for cloning, the ranges
> > make @@ -289,9 +291,11 @@ static int
> vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
> >   * If there's an error, then the usual negative error code is returned.
> >   * Otherwise returns 0 with *len set to the request length.
> >   */
> > -int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > -				  struct file *file_out, loff_t pos_out,
> > -				  loff_t *len, unsigned int remap_flags)
> > +static int
> > +__generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > +				struct file *file_out, loff_t pos_out,
> > +				loff_t *len, unsigned int remap_flags,
> > +				const struct iomap_ops *dax_read_ops)
> >  {
> >  	struct inode *inode_in = file_inode(file_in);
> >  	struct inode *inode_out = file_inode(file_out); @@ -351,8 +355,17 @@
> > int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> >  	if (remap_flags & REMAP_FILE_DEDUP) {
> >  		bool		is_same = false;
> >
> > -		ret = vfs_dedupe_file_range_compare(inode_in, pos_in,
> > -				inode_out, pos_out, *len, &is_same);
> > +		if (!IS_DAX(inode_in))
> > +			ret = vfs_dedupe_file_range_compare(inode_in, pos_in,
> > +					inode_out, pos_out, *len, &is_same); #ifdef
> CONFIG_FS_DAX
> > +		else if (dax_read_ops)
> > +			ret = dax_dedupe_file_range_compare(inode_in, pos_in,
> > +					inode_out, pos_out, *len, &is_same,
> > +					dax_read_ops);
> > +#endif /* CONFIG_FS_DAX */
> 
> Hmm, can you add an entry to the !IS_ENABLED(CONFIG_DAX) part of dax.h
> that defines dax_dedupe_file_range_compare as a dummy function that returns
> -EOPNOTSUPP?  We try not to sprinkle preprocessor directives into the middle
> of functions, per Linus rules.

I found that it's ok to build without the #ifdef and #endif here, even though CONFIG_FS_DAX is disabled.
And like other dax functions in fs/dax.c, such as dax_iomap_rw(), it is declared in include/linux/dax.h without IS_ENABLED() or #ifdef wrapped.  And xfs calls it directly and it won't cause build error.  So, I think I could just remove the #ifdef here, but I am not sure if this obeys the rule.

> 
> > +		else
> > +			return -EINVAL;
> >  		if (ret)
> >  			return ret;
> >  		if (!is_same)
> > @@ -370,6 +383,34 @@ int generic_remap_file_range_prep(struct file
> > *file_in, loff_t pos_in,
> >
> >  	return ret;
> >  }
> > +
> > +#ifdef CONFIG_FS_DAX
> > +int dax_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > +			      struct file *file_out, loff_t pos_out,
> > +			      loff_t *len, unsigned int remap_flags,
> > +			      const struct iomap_ops *ops) {
> > +	return __generic_remap_file_range_prep(file_in, pos_in, file_out,
> > +					       pos_out, len, remap_flags, ops); } #else int
> > +dax_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > +			      struct file *file_out, loff_t pos_out,
> > +			      loff_t *len, unsigned int remap_flags,
> > +			      const struct iomap_ops *ops) {
> > +	return -EOPNOTSUPP;
> > +}
> > +#endif /* CONFIG_FS_DAX */
> > +EXPORT_SYMBOL(dax_remap_file_range_prep);
> 
> I think this symbol belongs in fs/dax.c and the declaration in dax.h?

For the function name, it does should belong to fs/dax.  But if so, __generic_remap_file_range_prep() needs to be called in fs/dax.  I don't think this is good.


--
Thanks,
Ruan Shiyang.

> 
> --D
> 
> > +int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > +				  struct file *file_out, loff_t pos_out,
> > +				  loff_t *len, unsigned int remap_flags) {
> > +	return __generic_remap_file_range_prep(file_in, pos_in, file_out,
> > +					       pos_out, len, remap_flags, NULL); }
> >  EXPORT_SYMBOL(generic_remap_file_range_prep);
> >
> >  loff_t do_clone_file_range(struct file *file_in, loff_t pos_in, diff
> > --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c index
> > 060695d6d56a..d25434f93235 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -1329,8 +1329,12 @@ xfs_reflink_remap_prep(
> >  	if (IS_DAX(inode_in) || IS_DAX(inode_out))
> >  		goto out_unlock;
> >
> > -	ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
> > -			len, remap_flags);
> > +	if (!IS_DAX(inode_in))
> > +		ret = generic_remap_file_range_prep(file_in, pos_in, file_out,
> > +				pos_out, len, remap_flags);
> > +	else
> > +		ret = dax_remap_file_range_prep(file_in, pos_in, file_out,
> > +				pos_out, len, remap_flags, &xfs_read_iomap_ops);
> >  	if (ret || *len == 0)
> >  		goto out_unlock;
> >
> > diff --git a/include/linux/dax.h b/include/linux/dax.h index
> > 3275e01ed33d..32e1c34349f2 100644
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -239,6 +239,10 @@ int dax_invalidate_mapping_entry_sync(struct
> address_space *mapping,
> >  				      pgoff_t index);
> >  s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap,
> >  		struct iomap *srcmap);
> > +int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
> > +				  struct inode *dest, loff_t destoff,
> > +				  loff_t len, bool *is_same,
> > +				  const struct iomap_ops *ops);
> >  static inline bool dax_mapping(struct address_space *mapping)  {
> >  	return mapping->host && IS_DAX(mapping->host); diff --git
> > a/include/linux/fs.h b/include/linux/fs.h index
> > c3c88fdb9b2a..e2c348553d87 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -71,6 +71,7 @@ struct fsverity_operations;  struct fs_context;
> > struct fs_parameter_spec;  struct fileattr;
> > +struct iomap_ops;
> >
> >  extern void __init inode_init(void);
> >  extern void __init inode_init_early(void); @@ -2126,10 +2127,13 @@
> > extern ssize_t vfs_copy_file_range(struct file *, loff_t , struct file
> > *,  extern ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
> >  				       struct file *file_out, loff_t pos_out,
> >  				       size_t len, unsigned int flags); -extern int
> > generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > -					 struct file *file_out, loff_t pos_out,
> > -					 loff_t *count,
> > -					 unsigned int remap_flags);
> > +int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > +				  struct file *file_out, loff_t pos_out,
> > +				  loff_t *count, unsigned int remap_flags); int
> > +dax_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > +			      struct file *file_out, loff_t pos_out,
> > +			      loff_t *len, unsigned int remap_flags,
> > +			      const struct iomap_ops *ops);
> >  extern loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
> >  				  struct file *file_out, loff_t pos_out,
> >  				  loff_t len, unsigned int remap_flags);
> > --
> > 2.31.1
> >
> >
> >