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Message-ID: <20100423154713.GF2351@localhost.localdomain>
Date: Fri, 23 Apr 2010 11:47:14 -0400
From: Josef Bacik <josef@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Josef Bacik <josef@...hat.com>, akpm@...ux-foundation.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
randy.dunlap@...cle.com
Subject: Re: [PATCH] cleanup block based fiemap
On Fri, Apr 23, 2010 at 08:27:02AM -0700, Linus Torvalds wrote:
>
>
> On Fri, 23 Apr 2010, Josef Bacik wrote:
> >
> > __generic_block_fiemap is called by generic_block_fiemap which takes the
> > i_mutex. The only reason we have __generic_block_fiemap is because gfs2 needs
> > to do its own locking magic before we go calling get_block. The idea is that
> > the file size doesn't change while we're doing this.
>
> Ok, maybe just a comment then..
>
> > As for reading the size several times, I can read it once and store it in a
> > local variable if you prefer, but theres no way to know if len is smaller than
> > the size or not, which is why I'm constantly doing i_size_read(). If thats what
> > you would prefer I can do that, just let me know.
>
> .. or a comment _and_ a "read size once into a variable". Not a big deal,
> it just wasn't entirely clear to me and I hadn't checked the callchain.
>
> > > Issue #2: "blk_to_logical(inode, 0)"? WTF? Since when has shifting zero
> > > ever resulted in anything interesting or relevant? There's at least two of
> > > those things.
> > >
> >
> > Umm, yeah I'm sorry? I have no idea why I did that. I think its because I was
> > getting the logical offset of the first block + size, which is just stupid
> > because the logical offset is 0, so all I can say is I'm sorry that me a year
> > ago was alot dumber than me now :). Thanks,
>
> Ok, fix that, and I think the patch will be a clear improvement.
>
Great, here is the updated patch. Thanks for the review!
Josef
diff --git a/fs/ioctl.c b/fs/ioctl.c
index 6c75110..7faefb4 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -228,14 +228,23 @@ 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
- * @get_block - the fs's get_block function
+ * @inode: the inode to map
+ * @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
* through get_block until we hit the number of extents we want to map, or we
@@ -250,58 +259,63 @@ 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;
+ loff_t isize = i_size_read(inode);
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;
+ /*
+ * Either the i_mutex or other appropriate locking needs to be held
+ * since we expect isize to not change at all through the duration of
+ * this call.
+ */
+ if (len >= isize) {
+ whole_file = true;
+ len = isize;
+ }
- 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
* marked with FIEMAP_EXTENT_LAST
*/
if (!past_eof &&
- blk_to_logical(inode, start_blk) >=
- blk_to_logical(inode, 0)+i_size_read(inode))
+ blk_to_logical(inode, start_blk) >= isize)
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 +323,18 @@ 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 +348,7 @@ 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 +368,10 @@ 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);
/*
@@ -363,15 +379,13 @@ int __generic_block_fiemap(struct inode *inode,
* soon as we find a hole that the last extent we found
* is marked with FIEMAP_EXTENT_LAST
*/
- if (!past_eof &&
- logical+size >=
- blk_to_logical(inode, 0)+i_size_read(inode))
- past_eof = 1;
+ if (!past_eof && logical + size >= isize)
+ 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 39d57bc..44f35ae 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2315,8 +2315,9 @@ 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);
--
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