libfs: getdents() should return 0 after reaching EOD

[ Upstream commit 796432efab1e372d404e7a71cc6891a53f105051 ]

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. Seeking
resets the mark.

Reported-by: Tavian Barnes <tavianator@tavianator.com>
Closes: https://lore.kernel.org/linux-fsdevel/20231113180616.2831430-1-tavianator@tavianator.com/
Fixes: 6faddda69f62 ("libfs: Add directory operations for stable offsets")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/170043792492.4628.15646203084646716134.stgit@bazille.1015granger.net
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/libfs.c b/fs/libfs.c
index 37f2d34..189447c 100644 (file)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -396,6 +396,8 @@ static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence)
                return -EINVAL;
        }
 
+       /* In this case, ->private_data is protected by f_pos_lock */
+       file->private_data = NULL;
        return vfs_setpos(file, offset, U32_MAX);
 }
 
@@ -425,7 +427,7 @@ 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);
@@ -434,7 +436,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
        while (true) {
                dentry = offset_find_next(&xas);
                if (!dentry)
-                       break;
+                       return ERR_PTR(-ENOENT);
 
                if (!offset_dir_emit(ctx, dentry)) {
                        dput(dentry);
@@ -444,6 +446,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
                dput(dentry);
                ctx->pos = xas.xa_index + 1;
        }
+       return NULL;
 }
 
 /**
@@ -476,7 +479,12 @@ 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);
+       /* In this case, ->private_data is protected by f_pos_lock */
+       if (ctx->pos == 2)
+               file->private_data = NULL;
+       else if (file->private_data == ERR_PTR(-ENOENT))
+               return 0;
+       file->private_data = offset_iterate_dir(d_inode(dir), ctx);
        return 0;
 }