Re: [PATCH v2 2/5] btrfs: split btrfs_insert_delayed_dir_index() into prealloc and commit phases

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2026-08-05 at 08:44 +0930, 'Qu Wenruo' via Kernel Team wrote:
> 
> 在 2026/8/5 01:14, Jeff Layton 写道:
> > Split btrfs_insert_delayed_dir_index() into three functions using a new
> > btrfs_dir_index_prealloc struct to bundle the pre-allocated resources:
> > 
> > - btrfs_prealloc_delayed_dir_index(): performs the two GFP_NOFS
> >    allocations (delayed node + delayed item) that can fail with -ENOMEM.
> > - btrfs_insert_delayed_dir_index_prealloc(): populates the item data,
> >    inserts into the rb-tree, and reserves metadata space. Cannot fail
> >    with -ENOMEM since all allocations were done in the prealloc step.
> > - btrfs_free_delayed_dir_index_prealloc(): frees pre-allocated
> >    resources when the caller's btree insertion fails.
> > 
> > The original btrfs_insert_delayed_dir_index() is refactored into a thin
> > wrapper that calls the prealloc and commit functions.
> > 
> > This split allows callers to move the fallible memory allocations before
> > the point of no return (the DIR_ITEM btree insertion), so that -ENOMEM
> > can be returned cleanly without aborting the transaction.
> > 
> > Assisted-by: LLM
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >   fs/btrfs/delayed-inode.c | 111 +++++++++++++++++++++++++++++++++++++----------
> >   fs/btrfs/delayed-inode.h |  17 ++++++++
> >   2 files changed, 104 insertions(+), 24 deletions(-)
> > 
> > diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
> > index db2ffab0941a..95d2dca80444 100644
> > --- a/fs/btrfs/delayed-inode.c
> > +++ b/fs/btrfs/delayed-inode.c
> > @@ -6,6 +6,7 @@
> >   
> >   #include <linux/slab.h>
> >   #include <linux/iversion.h>
> > +#include <linux/error-injection.h>
> >   #include "ctree.h"
> >   #include "fs.h"
> >   #include "messages.h"
> > @@ -1469,35 +1470,74 @@ static void btrfs_release_dir_index_item_space(struct btrfs_trans_handle *trans)
> >   	trans->bytes_reserved -= bytes;
> >   }
> >   
> > -/* Will return 0, -ENOMEM or -EEXIST (index number collision, unexpected). */
> > -int btrfs_insert_delayed_dir_index(struct btrfs_trans_handle *trans,
> > -				   const char *name, int name_len,
> > -				   struct btrfs_inode *dir,
> > -				   const struct btrfs_disk_key *disk_key, u8 flags,
> > -				   u64 index)
> > +/*
> > + * Pre-allocate a delayed node and delayed item for a dir index insertion.
> > + * Call this before modifying the btree so that ENOMEM can be returned
> > + * before any on-disk state has changed.
> > + *
> > + * Returns 0 on success, -ENOMEM on allocation failure.
> > + */
> > +int btrfs_prealloc_delayed_dir_index(struct btrfs_inode *dir,
> > +				     const char *name, int name_len,
> > +				     struct btrfs_dir_index_prealloc *prealloc)
> 
> We can directly return a btrfs_dir_index_prealloc pointer, which reduce 
> the parameter list.
> 

...but then we'd have to allocate it separately. It's currently
allocated on the stack by the caller. I think we ought to keep it this
way, but I'm willing to be convinced otherwise.

> Otherwise looks good to me.
> 
> Reviewed-by: Qu Wenruo <wqu@suse.com>
> 

-- 
Jeff Layton <jlayton@kernel.org>