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authorChris Mason <chris.mason@oracle.com>2008-09-29 15:18:18 -0400
committerChris Mason <chris.mason@oracle.com>2008-09-29 15:18:18 -0400
commitd352ac68148b69937d39ca5d48bcc4478e118dbf (patch)
tree7951dd7311999d9e77766acdc7f8e93de97874d8 /fs/btrfs/file.c
parent9a5e1ea1e1e539e244a54afffc330fc368376ab9 (diff)
downloadop-kernel-dev-d352ac68148b69937d39ca5d48bcc4478e118dbf.zip
op-kernel-dev-d352ac68148b69937d39ca5d48bcc4478e118dbf.tar.gz
Btrfs: add and improve comments
This improves the comments at the top of many functions. It didn't dive into the guts of functions because I was trying to avoid merging problems with the new allocator and back reference work. extent-tree.c and volumes.c were both skipped, and there is definitely more work todo in cleaning and commenting the code. Signed-off-by: Chris Mason <chris.mason@oracle.com>
Diffstat (limited to 'fs/btrfs/file.c')
-rw-r--r--fs/btrfs/file.c44
1 files changed, 43 insertions, 1 deletions
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 1b7e51a..3088a11 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -41,6 +41,9 @@
#include "compat.h"
+/* simple helper to fault in pages and copy. This should go away
+ * and be replaced with calls into generic code.
+ */
static int noinline btrfs_copy_from_user(loff_t pos, int num_pages,
int write_bytes,
struct page **prepared_pages,
@@ -72,12 +75,19 @@ static int noinline btrfs_copy_from_user(loff_t pos, int num_pages,
return page_fault ? -EFAULT : 0;
}
+/*
+ * unlocks pages after btrfs_file_write is done with them
+ */
static void noinline btrfs_drop_pages(struct page **pages, size_t num_pages)
{
size_t i;
for (i = 0; i < num_pages; i++) {
if (!pages[i])
break;
+ /* page checked is some magic around finding pages that
+ * have been modified without going through btrfs_set_page_dirty
+ * clear it here
+ */
ClearPageChecked(pages[i]);
unlock_page(pages[i]);
mark_page_accessed(pages[i]);
@@ -85,6 +95,10 @@ static void noinline btrfs_drop_pages(struct page **pages, size_t num_pages)
}
}
+/* this does all the hard work for inserting an inline extent into
+ * the btree. Any existing inline extent is extended as required to make room,
+ * otherwise things are inserted as required into the btree
+ */
static int noinline insert_inline_extent(struct btrfs_trans_handle *trans,
struct btrfs_root *root, struct inode *inode,
u64 offset, size_t size,
@@ -228,6 +242,14 @@ fail:
return err;
}
+/*
+ * after copy_from_user, pages need to be dirtied and we need to make
+ * sure holes are created between the current EOF and the start of
+ * any next extents (if required).
+ *
+ * this also makes the decision about creating an inline extent vs
+ * doing real data extents, marking pages dirty and delalloc as required.
+ */
static int noinline dirty_and_release_pages(struct btrfs_trans_handle *trans,
struct btrfs_root *root,
struct file *file,
@@ -362,6 +384,10 @@ out_unlock:
return err;
}
+/*
+ * this drops all the extents in the cache that intersect the range
+ * [start, end]. Existing extents are split as required.
+ */
int btrfs_drop_extent_cache(struct inode *inode, u64 start, u64 end,
int skip_pinned)
{
@@ -536,6 +562,9 @@ out:
* If an extent intersects the range but is not entirely inside the range
* it is either truncated or split. Anything entirely inside the range
* is deleted from the tree.
+ *
+ * inline_limit is used to tell this code which offsets in the file to keep
+ * if they contain inline extents.
*/
int noinline btrfs_drop_extents(struct btrfs_trans_handle *trans,
struct btrfs_root *root, struct inode *inode,
@@ -796,7 +825,9 @@ out:
}
/*
- * this gets pages into the page cache and locks them down
+ * this gets pages into the page cache and locks them down, it also properly
+ * waits for data=ordered extents to finish before allowing the pages to be
+ * modified.
*/
static int noinline prepare_pages(struct btrfs_root *root, struct file *file,
struct page **pages, size_t num_pages,
@@ -1034,6 +1065,17 @@ int btrfs_release_file(struct inode * inode, struct file * filp)
return 0;
}
+/*
+ * fsync call for both files and directories. This logs the inode into
+ * the tree log instead of forcing full commits whenever possible.
+ *
+ * It needs to call filemap_fdatawait so that all ordered extent updates are
+ * in the metadata btree are up to date for copying to the log.
+ *
+ * It drops the inode mutex before doing the tree log commit. This is an
+ * important optimization for directories because holding the mutex prevents
+ * new operations on the dir while we write to disk.
+ */
int btrfs_sync_file(struct file *file, struct dentry *dentry, int datasync)
{
struct inode *inode = dentry->d_inode;
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