Re: [PATCH] cleanup __generic_block_fiemap and fix a few minor issues

[Josef Bacik <josef@redhat.com>]

On Thu, Mar 04, 2010 at 08:03:55AM -0800, Linus Torvalds wrote:
> 
> 
> On Wed, 3 Mar 2010, Josef Bacik wrote:
> > 
> > 1) Some filesystems (gfs2) do not like being given non-block-aligned b_size's to
> > map, so make sure we block align the b_size.
> 
> As far as I can tell, that alignment is wrong.
> 
> You can't just align "len". If "start" wasn't aligned, then just aligning 
> "len" is wrong. And if start is guaranteed to be aligned, how?
> 

Hmm I said that wrong.  GFS2 can't handle < blocksize map requests, so making
the length blocksize aligned fixed that problem, I just described it wrong.

> Also, the alignment itself is ugly as hell, doing
> 
> > +	len = (len + (1 << inode->i_blkbits) - 1) &
> > +		~((1 << inode->i_blkbits) - 1);
> > +	map_end = start + len;
> 
> When what you probably should have done is to do
> 
> 	map_end = start + len;
> 
> _before_ rounding 'start', and then after that you can now map 'start' and 
> 'map_end' just using the regular "logical_to_blk" that you already use (up 
> or down depending on whether the thing should be inclusive or exclusive of 
> partial blocks). No?
> 
> IOW, the whole thing should probably look something like
> 
> 	sector_t start_blk, last_blk;
> 
> 	start_blk = logical_to_blk(inode, start);
> 	last_blk = logical_to_blk(inode, start + len - 1);
> 
> and you're done. Short, sweet, and to the point (note that "last_blk" 
> really is the _last_ block, so if you want the length in blocks, it would 
> be "last_blk - start_blk + 1").
> 

Ahh yes thats much nicer, thank you.  Here is my updated patch with your
suggestions.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
---
 fs/ioctl.c         |   81 +++++++++++++++++++++++++++++----------------------
 include/linux/fs.h |    5 ++-
 2 files changed, 49 insertions(+), 37 deletions(-)

diff --git a/fs/ioctl.c b/fs/ioctl.c
index 6c75110..64fed0b 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -228,13 +228,22 @@ static int ioctl_fiemap(struct file *filp, unsigned long arg)
 
 #ifdef CONFIG_BLOCK
 
-#define blk_to_logical(inode, blk) (blk << (inode)->i_blkbits)
-#define logical_to_blk(inode, offset) (offset >> (inode)->i_blkbits);
+static inline sector_t logical_to_blk(struct inode *inode, loff_t offset)
+{
+	return (offset >> inode->i_blkbits);
+}
+
+static inline loff_t blk_to_logical(struct inode *inode, sector_t blk)
+{
+	return (blk << inode->i_blkbits);
+}
 
 /**
  * __generic_block_fiemap - FIEMAP for block based inodes (no locking)
  * @inode - the inode to map
- * @arg - the pointer to userspace where we copy everything to
+ * @fieinfo - the fiemap info struct that will be passed back to userspace
+ * @start - where to start mapping in the inode
+ * @len - how much space to map
  * @get_block - the fs's get_block function
  *
  * This does FIEMAP for block based inodes.  Basically it will just loop
@@ -250,46 +259,46 @@ static int ioctl_fiemap(struct file *filp, unsigned long arg)
  */
 
 int __generic_block_fiemap(struct inode *inode,
-			   struct fiemap_extent_info *fieinfo, u64 start,
-			   u64 len, get_block_t *get_block)
+			   struct fiemap_extent_info *fieinfo, loff_t start,
+			   loff_t len, get_block_t *get_block)
 {
-	struct buffer_head tmp;
-	unsigned long long start_blk;
-	long long length = 0, map_len = 0;
+	struct buffer_head map_bh;
+	sector_t start_blk, last_blk;
 	u64 logical = 0, phys = 0, size = 0;
 	u32 flags = FIEMAP_EXTENT_MERGED;
-	int ret = 0, past_eof = 0, whole_file = 0;
+	bool past_eof = false, whole_file = false;
+	int ret = 0;
 
-	if ((ret = fiemap_check_flags(fieinfo, FIEMAP_FLAG_SYNC)))
+	ret = fiemap_check_flags(fieinfo, FIEMAP_FLAG_SYNC);
+	if (ret)
 		return ret;
 
-	start_blk = logical_to_blk(inode, start);
-
-	length = (long long)min_t(u64, len, i_size_read(inode));
-	if (length < len)
-		whole_file = 1;
+	if (len >= i_size_read(inode)) {
+		whole_file = true;
+		len = i_size_read(inode);
+	}
 
-	map_len = length;
+	start_blk = logical_to_blk(inode, start);
+	last_blk = logical_to_blk(inode, start + len - 1);
 
 	do {
 		/*
 		 * we set b_size to the total size we want so it will map as
 		 * many contiguous blocks as possible at once
 		 */
-		memset(&tmp, 0, sizeof(struct buffer_head));
-		tmp.b_size = map_len;
+		memset(&map_bh, 0, sizeof(struct buffer_head));
+		map_bh.b_size = len;
 
-		ret = get_block(inode, start_blk, &tmp, 0);
+		ret = get_block(inode, start_blk, &map_bh, 0);
 		if (ret)
 			break;
 
 		/* HOLE */
-		if (!buffer_mapped(&tmp)) {
-			length -= blk_to_logical(inode, 1);
+		if (!buffer_mapped(&map_bh)) {
 			start_blk++;
 
 			/*
-			 * we want to handle the case where there is an
+			 * We want to handle the case where there is an
 			 * allocated block at the front of the file, and then
 			 * nothing but holes up to the end of the file properly,
 			 * to make sure that extent at the front gets properly
@@ -297,11 +306,11 @@ int __generic_block_fiemap(struct inode *inode,
 			 */
 			if (!past_eof &&
 			    blk_to_logical(inode, start_blk) >=
-			    blk_to_logical(inode, 0)+i_size_read(inode))
+			    blk_to_logical(inode, 0) + i_size_read(inode))
 				past_eof = 1;
 
 			/*
-			 * first hole after going past the EOF, this is our
+			 * First hole after going past the EOF, this is our
 			 * last extent
 			 */
 			if (past_eof && size) {
@@ -309,15 +318,18 @@ int __generic_block_fiemap(struct inode *inode,
 				ret = fiemap_fill_next_extent(fieinfo, logical,
 							      phys, size,
 							      flags);
-				break;
+			} else if (size) {
+				ret = fiemap_fill_next_extent(fieinfo, logical,
+							      phys, size, flags);
+				size = 0;
 			}
 
 			/* if we have holes up to/past EOF then we're done */
-			if (length <= 0 || past_eof)
+			if (start_blk > last_blk || past_eof || ret)
 				break;
 		} else {
 			/*
-			 * we have gone over the length of what we wanted to
+			 * We have gone over the length of what we wanted to
 			 * map, and it wasn't the entire file, so add the extent
 			 * we got last time and exit.
 			 *
@@ -331,7 +343,7 @@ int __generic_block_fiemap(struct inode *inode,
 			 * are good to go, just add the extent to the fieinfo
 			 * and break
 			 */
-			if (length <= 0 && !whole_file) {
+			if (start_blk > last_blk && !whole_file) {
 				ret = fiemap_fill_next_extent(fieinfo, logical,
 							      phys, size,
 							      flags);
@@ -351,11 +363,10 @@ int __generic_block_fiemap(struct inode *inode,
 			}
 
 			logical = blk_to_logical(inode, start_blk);
-			phys = blk_to_logical(inode, tmp.b_blocknr);
-			size = tmp.b_size;
+			phys = blk_to_logical(inode, map_bh.b_blocknr);
+			size = map_bh.b_size;
 			flags = FIEMAP_EXTENT_MERGED;
 
-			length -= tmp.b_size;
 			start_blk += logical_to_blk(inode, size);
 
 			/*
@@ -364,14 +375,14 @@ int __generic_block_fiemap(struct inode *inode,
 			 * is marked with FIEMAP_EXTENT_LAST
 			 */
 			if (!past_eof &&
-			    logical+size >=
-			    blk_to_logical(inode, 0)+i_size_read(inode))
-				past_eof = 1;
+			    logical + size >=
+			    blk_to_logical(inode, 0) + i_size_read(inode))
+				past_eof = true;
 		}
 		cond_resched();
 	} while (1);
 
-	/* if ret is 1 then we just hit the end of the extent array */
+	/* If ret is 1 then we just hit the end of the extent array */
 	if (ret == 1)
 		ret = 0;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ebb1cd5..7e6e47f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2313,8 +2313,9 @@ extern int vfs_fstatat(int , char __user *, struct kstat *, int);
 extern int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd,
 		    unsigned long arg);
 extern int __generic_block_fiemap(struct inode *inode,
-				  struct fiemap_extent_info *fieinfo, u64 start,
-				  u64 len, get_block_t *get_block);
+				  struct fiemap_extent_info *fieinfo,
+				  loff_t start, loff_t len,
+				  get_block_t *get_block);
 extern int generic_block_fiemap(struct inode *inode,
 				struct fiemap_extent_info *fieinfo, u64 start,
 				u64 len, get_block_t *get_block);
-- 
1.6.5.rc2