linux-kernel - [PATCH v2] bcachefs: bch2_dir_emit() - fix directory reads in the fuse driver

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Date: Fri, 31 May 2024 00:13:58 +0300
From: Ariel Miculas <ariel.miculas@...il.com>
To: linux-bcachefs@...r.kernel.org
Cc: Ariel Miculas <ariel.miculas@...il.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Brian Foster <bfoster@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] bcachefs: bch2_dir_emit() - fix directory reads in the fuse driver

Commit 0c0cbfdb84725e9933a24ecf47c61bdeeda06ba2 dropped the ctx->pos
update before the call to dir_emit. This breaks the userspace
implementation, causing the directory reads to be stuck in an infinite
loop. This doesn't happen in the kernel because the vfs handles the
updates to ctx->pos, but in the fuse implementation nobody updates
it.

Signed-off-by: Ariel Miculas <ariel.miculas@...il.com>
---
V1 -> V2:
- added a comment explaining why the update to ctx->pos is necessary

 fs/bcachefs/dirent.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/bcachefs/dirent.c b/fs/bcachefs/dirent.c
index c67460d8205d..d743da89308e 100644
--- a/fs/bcachefs/dirent.c
+++ b/fs/bcachefs/dirent.c
@@ -534,6 +534,14 @@ int bch2_empty_dir_trans(struct btree_trans *trans, subvol_inum dir)
 static int bch2_dir_emit(struct dir_context *ctx, struct bkey_s_c_dirent d, subvol_inum target)
 {
 	struct qstr name = bch2_dirent_get_name(d);
+	/*
+	 * Although not required by the kernel code, updating ctx->pos is needed
+	 * for the bcachefs FUSE driver. Without this update, the FUSE
+	 * implementation will be stuck in an infinite loop when reading
+	 * directories (via the bcachefs_fuse_readdir callback).
+	 * In kernel space, ctx->pos is updated by the VFS code.
+	 */
+	ctx->pos = d.k->p.offset;
 	bool ret = dir_emit(ctx, name.name,
 		      name.len,
 		      target.inum,
-- 
2.34.1