IO-Uring Archive on lore.kernel.org
 help / color / Atom feed
From: Jens Axboe <axboe@kernel.dk>
To: io-uring@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
	Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 1/6] fs: add namei support for doing a non-blocking path lookup
Date: Tue,  7 Jan 2020 10:00:29 -0700
Message-ID: <20200107170034.16165-2-axboe@kernel.dk> (raw)
In-Reply-To: <20200107170034.16165-1-axboe@kernel.dk>

If the fast lookup fails, then return -EAGAIN to have the caller retry
the path lookup. Assume that a dentry having any of:

->d_revalidate()
->d_automount()
->d_manage()

could block in those callbacks. Preemptively return -EAGAIN if any of
these are present.

This is in preparation for supporting non-blocking open.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/namei.c            | 21 ++++++++++++++++++++-
 include/linux/namei.h |  2 ++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index b367fdb91682..ed108a41634f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1641,6 +1641,17 @@ static struct dentry *__lookup_hash(const struct qstr *name,
 	return dentry;
 }
 
+static inline bool lookup_could_block(struct dentry *dentry, unsigned int flags)
+{
+	const struct dentry_operations *ops = dentry->d_op;
+
+	if (!ops || !(flags & LOOKUP_NONBLOCK))
+		return 0;
+
+	/* assume these dentry ops may block */
+	return ops->d_revalidate || ops->d_automount || ops->d_manage;
+}
+
 static int lookup_fast(struct nameidata *nd,
 		       struct path *path, struct inode **inode,
 		       unsigned *seqp)
@@ -1665,6 +1676,9 @@ static int lookup_fast(struct nameidata *nd,
 			return 0;
 		}
 
+		if (unlikely(lookup_could_block(dentry, nd->flags)))
+			return -EAGAIN;
+
 		/*
 		 * This sequence count validates that the inode matches
 		 * the dentry name information from lookup.
@@ -1707,7 +1721,10 @@ static int lookup_fast(struct nameidata *nd,
 		dentry = __d_lookup(parent, &nd->last);
 		if (unlikely(!dentry))
 			return 0;
-		status = d_revalidate(dentry, nd->flags);
+		if (unlikely(lookup_could_block(dentry, nd->flags)))
+			status = -EAGAIN;
+		else
+			status = d_revalidate(dentry, nd->flags);
 	}
 	if (unlikely(status <= 0)) {
 		if (!status)
@@ -1912,6 +1929,8 @@ static int walk_component(struct nameidata *nd, int flags)
 	if (unlikely(err <= 0)) {
 		if (err < 0)
 			return err;
+		if (nd->flags & LOOKUP_NONBLOCK)
+			return -EAGAIN;
 		path.dentry = lookup_slow(&nd->last, nd->path.dentry,
 					  nd->flags);
 		if (IS_ERR(path.dentry))
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 4e77068f7a1a..392eb439f88b 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -49,6 +49,8 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
 /* LOOKUP_* flags which do scope-related checks based on the dirfd. */
 #define LOOKUP_IS_SCOPED (LOOKUP_BENEATH | LOOKUP_IN_ROOT)
 
+#define LOOKUP_NONBLOCK		0x200000 /* don't block for lookup */
+
 extern int path_pts(struct path *path);
 
 extern int user_path_at_empty(int, const char __user *, unsigned, struct path *, int *empty);
-- 
2.24.1


  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-07 17:00 [PATCHSET v2 0/6] io_uring: add support for open/close Jens Axboe
2020-01-07 17:00 ` Jens Axboe [this message]
2020-01-25 13:15   ` [PATCH 1/6] fs: add namei support for doing a non-blocking path lookup Jeff Layton
2020-01-07 17:00 ` [PATCH 2/6] fs: make build_open_flags() available internally Jens Axboe
2020-01-07 17:00 ` [PATCH 3/6] io_uring: add support for IORING_OP_OPENAT Jens Axboe
2020-01-08 13:05   ` Stefan Metzmacher
2020-01-08 16:20     ` Jens Axboe
2020-01-08 16:32       ` Stefan Metzmacher
2020-01-08 16:40         ` Jens Axboe
2020-01-08 17:04           ` Stefan Metzmacher
2020-01-08 22:53             ` Jens Axboe
2020-01-08 23:03               ` Stefan Metzmacher
2020-01-08 23:05                 ` Jens Axboe
2020-01-08 23:11                   ` Stefan Metzmacher
2020-01-08 23:22                     ` Jens Axboe
2020-01-09 10:40                       ` Stefan Metzmacher
2020-01-09 21:31                         ` Jens Axboe
2020-01-16 22:42                           ` Stefan Metzmacher
2020-01-17  0:16                             ` Jens Axboe
2020-01-07 17:00 ` [PATCH 4/6] fs: move filp_close() outside of __close_fd_get_file() Jens Axboe
2020-01-07 17:00 ` [PATCH 5/6] io-wq: add support for uncancellable work Jens Axboe
2020-01-07 17:00 ` [PATCH 6/6] io_uring: add support for IORING_OP_CLOSE Jens Axboe
2020-01-08 21:17 ` [PATCHSET v2 0/6] io_uring: add support for open/close Stefan Metzmacher
2020-01-08 22:57   ` Jens Axboe
2020-01-08 23:05     ` Stefan Metzmacher
2020-01-09  1:02       ` Jens Axboe
2020-01-09  2:03         ` Jens Axboe
2020-01-16 22:50           ` Stefan Metzmacher
2020-01-17  0:18             ` Jens Axboe
2020-01-20 12:15               ` Stefan Metzmacher
2020-01-20 13:04                 ` Pavel Begunkov
2020-01-17  0:44             ` Colin Walters
2020-01-17  0:51               ` Jens Axboe
2020-01-17  9:32               ` Pavel Begunkov
2020-01-17 15:21                 ` Jens Axboe
2020-01-17 22:27                   ` Pavel Begunkov
2020-01-17 22:36                     ` Jens Axboe

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200107170034.16165-2-axboe@kernel.dk \
    --to=axboe@kernel.dk \
    --cc=io-uring@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=viro@zeniv.linux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

IO-Uring Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/io-uring/0 io-uring/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 io-uring io-uring/ https://lore.kernel.org/io-uring \
		io-uring@vger.kernel.org
	public-inbox-index io-uring

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.io-uring


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git