linux-kernel - [PATCH v2 2/6] vfs_getdents/struct dir

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Message-Id: <20230422-uring-getdents-v2-2-2db1e37dc55e@codewreck.org>
Date:   Wed, 10 May 2023 19:52:50 +0900
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>,
        Stefan Roesch <shr@...com>
Cc:     Clay Harris <bugs@...ycon.org>, Dave Chinner <david@...morbit.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        io-uring@...r.kernel.org,
        Dominique Martinet <asmadeus@...ewreck.org>
Subject: [PATCH v2 2/6] vfs_getdents/struct dir_context: add flags field

The flags will allow passing DIR_CONTEXT_F_NOWAIT to iterate()
implementations that support it (as signaled through FMODE_NWAIT
in file->f_mode)

Notes:
- considered using IOCB_NOWAIT but if we add more flags later it
would be confusing to keep track of which values are valid, use
dedicated flags
- might want to check ctx.flags & DIR_CONTEXT_F_NOWAIT is only set
when file->f_mode & FMODE_NOWAIT in iterate_dir() as e.g. WARN_ONCE?

Signed-off-by: Dominique Martinet <asmadeus@...ewreck.org>
---
 fs/internal.h      | 2 +-
 fs/readdir.c       | 6 ++++--
 include/linux/fs.h | 8 ++++++++
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index e8ca000e6613..0264b001d99a 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -267,4 +267,4 @@ void mnt_idmap_put(struct mnt_idmap *idmap);
 struct linux_dirent64;
 
 int vfs_getdents(struct file *file, struct linux_dirent64 __user *dirent,
-		 unsigned int count);
+		 unsigned int count, unsigned long flags);
diff --git a/fs/readdir.c b/fs/readdir.c
index ed0803d0011e..1311b89d75e1 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -358,12 +358,14 @@ static bool filldir64(struct dir_context *ctx, const char *name, int namlen,
  * @file    : pointer to file struct of directory
  * @dirent  : pointer to user directory structure
  * @count   : size of buffer
+ * @flags   : additional dir_context flags
  */
 int vfs_getdents(struct file *file, struct linux_dirent64 __user *dirent,
-		 unsigned int count)
+		 unsigned int count, unsigned long flags)
 {
 	struct getdents_callback64 buf = {
 		.ctx.actor = filldir64,
+		.ctx.flags = flags,
 		.count = count,
 		.current_dir = dirent
 	};
@@ -395,7 +397,7 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 	if (!f.file)
 		return -EBADF;
 
-	error = vfs_getdents(f.file, dirent, count);
+	error = vfs_getdents(f.file, dirent, count, 0);
 
 	fdput_pos(f);
 	return error;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 21a981680856..f7de2b5ca38e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1716,8 +1716,16 @@ typedef bool (*filldir_t)(struct dir_context *, const char *, int, loff_t, u64,
 struct dir_context {
 	filldir_t actor;
 	loff_t pos;
+	unsigned long flags;
 };
 
+/*
+ * flags for dir_context flags
+ * DIR_CONTEXT_F_NOWAIT: Request non-blocking iterate
+ *                       (requires file->f_mode & FMODE_NOWAIT)
+ */
+#define DIR_CONTEXT_F_NOWAIT	0x1
+
 /*
  * These flags let !MMU mmap() govern direct device mapping vs immediate
  * copying more easily for MAP_PRIVATE, especially for ROM filesystems.

-- 
2.39.2