IO-Uring Archive on lore.kernel.org
 help / color / Atom feed
From: Jeff Layton <jlayton@kernel.org>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: [PATCH 1/6] fs: add namei support for doing a non-blocking path lookup
Date: Sat, 25 Jan 2020 08:15:01 -0500
Message-ID: <c49d8fb5f7a056cddfa19f9b48af878ac14536d2.camel@kernel.org> (raw)
In-Reply-To: <20200107170034.16165-2-axboe@kernel.dk>

On Tue, 2020-01-07 at 10:00 -0700, Jens Axboe wrote:
> 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;
> +}
> +

d_revalidate shouldn't block if LOOKUP_RCU is set.


>  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);

-- 
Jeff Layton <jlayton@kernel.org>


  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 ` [PATCH 1/6] fs: add namei support for doing a non-blocking path lookup Jens Axboe
2020-01-25 13:15   ` Jeff Layton [this message]
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 publicly 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=c49d8fb5f7a056cddfa19f9b48af878ac14536d2.camel@kernel.org \
    --to=jlayton@kernel.org \
    --cc=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