[PATCH RFC] libfs: getdents() should return 0 after reaching EOD

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From: Chuck Lever <chuck.lever@xxxxxxxxxx>

The new directory offset helpers don't conform with the convention
of getdents() returning no more entries once a directory file
descriptor has reached the current end-of-directory.

To address this, copy the logic from dcache_readdir() to mark the
open directory file descriptor once EOD has been reached. Rewinding
resets the mark.

Reported-by: Tavian Barnes <tavianator@xxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/linux-fsdevel/20231113180616.2831430-1-tavianator@xxxxxxxxxxxxxx/
Fixes: 6faddda69f62 ("libfs: Add directory operations for stable offsets")
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 fs/libfs.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index e9440d55073c..1c866b087f0c 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -428,7 +428,7 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry)
 			  inode->i_ino, fs_umode_to_dtype(inode->i_mode));
 }
 
-static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
+static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
 {
 	struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode);
 	XA_STATE(xas, &so_ctx->xa, ctx->pos);
@@ -437,7 +437,8 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
 	while (true) {
 		dentry = offset_find_next(&xas);
 		if (!dentry)
-			break;
+			/* readdir has reached the current EOD */
+			return (void *)0x10;
 
 		if (!offset_dir_emit(ctx, dentry)) {
 			dput(dentry);
@@ -447,6 +448,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
 		dput(dentry);
 		ctx->pos = xas.xa_index + 1;
 	}
+	return NULL;
 }
 
 /**
@@ -479,7 +481,12 @@ static int offset_readdir(struct file *file, struct dir_context *ctx)
 	if (!dir_emit_dots(file, ctx))
 		return 0;
 
-	offset_iterate_dir(d_inode(dir), ctx);
+	if (ctx->pos == 2)
+		file->private_data = NULL;
+	else if (file->private_data == (void *)0x10)
+		return 0;
+
+	file->private_data = offset_iterate_dir(d_inode(dir), ctx);
 	return 0;
 }
 






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