Linux-Fsdevel Archive on lore.kernel.org
 help / color / Atom feed
From: Christian Brauner <christian.brauner@ubuntu.com>
To: Matthew Bobrowski <repnop@google.com>
Cc: jack@suse.cz, amir73il@gmail.com, linux-api@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/2] fanotify: Add pidfd support to the fanotify API
Date: Mon, 19 Apr 2021 15:20:20 +0200
Message-ID: <20210419132020.ydyb2ly6e3clhe2j@wittgenstein> (raw)
In-Reply-To: <e6cd967f45381d20d67c9d5a3e49e3cb9808f65b.1618527437.git.repnop@google.com>

On Fri, Apr 16, 2021 at 09:22:25AM +1000, Matthew Bobrowski wrote:
> Introduce a new flag FAN_REPORT_PIDFD for fanotify_init(2) which
> allows userspace applications to control whether a pidfd is to be
> returned instead of a pid for `struct fanotify_event_metadata.pid`.
> 
> FAN_REPORT_PIDFD is mutually exclusive with FAN_REPORT_TID as the
> pidfd API is currently restricted to only support pidfd generation for
> thread-group leaders. Attempting to set them both when calling
> fanotify_init(2) will result in -EINVAL being returned to the
> caller. As the pidfd API evolves and support is added for tids, this
> is something that could be relaxed in the future.
> 
> If pidfd creation fails, the pid in struct fanotify_event_metadata is
> set to FAN_NOPIDFD(-1). Falling back and providing a pid instead of a
> pidfd on pidfd creation failures was considered, although this could
> possibly lead to confusion and unpredictability within userspace
> applications as distinguishing between whether an actual pidfd or pid
> was returned could be difficult, so it's best to be explicit.
> 
> Signed-off-by: Matthew Bobrowski <repnop@google.com>
> ---
>  fs/notify/fanotify/fanotify_user.c | 33 +++++++++++++++++++++++++++---
>  include/linux/fanotify.h           |  2 +-
>  include/uapi/linux/fanotify.h      |  2 ++
>  3 files changed, 33 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index 9e0c1afac8bd..fd8ae88796a8 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -329,7 +329,7 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
>  	struct fanotify_info *info = fanotify_event_info(event);
>  	unsigned int fid_mode = FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS);
>  	struct file *f = NULL;
> -	int ret, fd = FAN_NOFD;
> +	int ret, pidfd, fd = FAN_NOFD;
>  	int info_type = 0;
>  
>  	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
> @@ -340,7 +340,25 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
>  	metadata.vers = FANOTIFY_METADATA_VERSION;
>  	metadata.reserved = 0;
>  	metadata.mask = event->mask & FANOTIFY_OUTGOING_EVENTS;
> -	metadata.pid = pid_vnr(event->pid);
> +
> +	if (FAN_GROUP_FLAG(group, FAN_REPORT_PIDFD) &&
> +		pid_has_task(event->pid, PIDTYPE_TGID)) {
> +		/*
> +		 * Given FAN_REPORT_PIDFD is to be mutually exclusive with
> +		 * FAN_REPORT_TID, panic here if the mutual exclusion is ever
> +		 * blindly lifted without pidfds for threads actually being
> +		 * supported.
> +		 */
> +		WARN_ON(FAN_GROUP_FLAG(group, FAN_REPORT_TID));
> +
> +		pidfd = pidfd_create(event->pid, 0);
> +		if (unlikely(pidfd < 0))
> +			metadata.pid = FAN_NOPIDFD;
> +		else
> +			metadata.pid = pidfd;

I'm not a fan of overloading fields (Yes, we did this for the _legacy_
clone() syscall for CLONE_PIDFD/CLONE_PARENT_SETTID but in general it's
never a good idea if there are other options, imho.).
Could/should we consider the possibility of adding a new pidfd field to
struct fanotify_event_metadata?

Christian

  parent reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15 23:21 [PATCH 0/2] fanotify: Adding " Matthew Bobrowski
2021-04-15 23:22 ` [PATCH 1/2] pidfd_create(): remove static qualifier and declare pidfd_create() in linux/pid.h Matthew Bobrowski
2021-04-19 10:13   ` Jan Kara
2021-04-19 12:50   ` Christian Brauner
2021-04-20  0:17     ` Matthew Bobrowski
2021-04-15 23:22 ` [PATCH 2/2] fanotify: Add pidfd support to the fanotify API Matthew Bobrowski
2021-04-16  6:27   ` Amir Goldstein
2021-04-16  7:05     ` Matthew Bobrowski
2021-04-16  7:53       ` Amir Goldstein
2021-04-16  8:08         ` Matthew Bobrowski
2021-04-19 13:02     ` Christian Brauner
2021-04-19 10:21   ` Jan Kara
2021-04-20  1:35     ` Matthew Bobrowski
2021-04-19 13:20   ` Christian Brauner [this message]
2021-04-19 13:53     ` Amir Goldstein
2021-04-19 14:44       ` Christian Brauner
2021-04-19 13:55     ` Jan Kara
2021-04-19 15:02       ` Christian Brauner
2021-04-20  2:36         ` Matthew Bobrowski
2021-04-21  8:04           ` Jan Kara
2021-04-21  9:29             ` Amir Goldstein
2021-04-21 10:00               ` Jan Kara
2021-04-21 10:12                 ` Amir Goldstein
2021-04-21 13:48                   ` Jan Kara
2021-04-21 14:46                     ` Christian Brauner
2021-04-22 23:06             ` Matthew Bobrowski
2021-04-23  7:39               ` Amir Goldstein
2021-04-23  8:02                 ` Matthew Bobrowski
2021-04-23  8:14                   ` Amir Goldstein
2021-04-26 10:26                     ` Matthew Bobrowski
2021-04-26 11:11                       ` Amir Goldstein
2021-04-27  3:35                         ` Matthew Bobrowski
2021-04-27  5:14                           ` Amir Goldstein
2021-04-28 22:53                             ` Matthew Bobrowski
2021-04-19 12:34 ` [PATCH 0/2] fanotify: Adding " Christian Brauner

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=20210419132020.ydyb2ly6e3clhe2j@wittgenstein \
    --to=christian.brauner@ubuntu.com \
    --cc=amir73il@gmail.com \
    --cc=jack@suse.cz \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=repnop@google.com \
    /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

Linux-Fsdevel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/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 linux-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \
		linux-fsdevel@vger.kernel.org
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-fsdevel


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