From: Karel Zak <kzak@redhat.com>
To: Christian Brauner <brauner@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
linux-fsdevel@vger.kernel.org, Dave Chinner <david@fromorbit.com>,
Theodore Ts'o <tytso@mit.edu>,
Greg KH <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org,
Linux API <linux-api@vger.kernel.org>,
linux-man <linux-man@vger.kernel.org>,
LSM <linux-security-module@vger.kernel.org>,
Ian Kent <raven@themaw.net>, David Howells <dhowells@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <christian@brauner.io>,
Amir Goldstein <amir73il@gmail.com>,
James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [RFC PATCH] getting misc stats/attributes via xattr API
Date: Tue, 10 May 2022 14:35:12 +0200 [thread overview]
Message-ID: <20220510123512.h6jjqgowex6gnjh5@ws.net.home> (raw)
In-Reply-To: <20220509124815.vb7d2xj5idhb2wq6@wittgenstein>
On Mon, May 09, 2022 at 02:48:15PM +0200, Christian Brauner wrote:
> One comment about this. We really need to have this interface support
> giving us mount options like "relatime" back in numeric form (I assume
> this will be possible.). It is royally annoying having to maintain a
> mapping table in userspace just to do:
>
> relatime -> MS_RELATIME/MOUNT_ATTR_RELATIME
> ro -> MS_RDONLY/MOUNT_ATTR_RDONLY
>
> A library shouldn't be required to use this interface. Conservative
> low-level software that keeps its shared library dependencies minimal
> will need to be able to use that interface without having to go to an
> external library that transforms text-based output to binary form (Which
> I'm very sure will need to happen if we go with a text-based
> interface.).
Sounds like David's fsinfo() :-)
We need an interface where the kernel returns a consistent mount table
entry (more syscalls to get more key=value could be a way how to get
inconsistent data).
IMHO all the attempts to make a trivial interface will be unsuccessful
because the mount table is complex (tree) and mixes strings, paths,
and flags. We will always end with a complex interface or complex
strings (like the last xatts attempt). There is no 3rd path to go ...
The best would be simplified fsinfo() where userspace defines
a request (wanted "keys"), and the kernel fills a buffer with data
separated by some header metadata struct. In this case, the kernel can
return strings and structs with binary data.
I'd love something like:
ssize_t sz;
fsinfo_query query[] = {
{ .request = FSINFO_MOUNT_PATH },
{ .request = FSINFO_PROPAGATION },
{ .request = FSINFO_CHILDREN_IDS },
};
sz = fsinfo(dfd, "", AT_EMPTY_PATH,
&query, ARRAY_SIZE(query),
buf, sizeof(buf));
for (p = buf; p < buf + sz; ) {
{
fsinfo_entry *e = (struct fsinfo_entry) p;
char *data = p + sizeof(struct fsinfo_entry);
switch(e->request) {
case FSINFO_MOUNT_PATH:
printf("mountpoint %s\n", data);
break;
case FSINFO_PROPAGATION:
printf("propagation %x\n", (uintptr_t) data);
break;
case FSINFO_CHILDREN_IDS:
fsinfo_child *x = (fsinfo_child *) data;
for (i = 0; i < e->count; i++) {
printf("child: %d\n", x[i].mnt_id);
}
break;
...
}
p += sizeof(struct fsinfo_entry) + e->len;
}
... my two cents :-)
Karel
--
Karel Zak <kzak@redhat.com>
http://karelzak.blogspot.com
next prev parent reply other threads:[~2022-05-10 12:35 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-03 12:23 [RFC PATCH] getting misc stats/attributes via xattr API Miklos Szeredi
2022-05-03 14:39 ` Amir Goldstein
2022-05-03 14:53 ` Greg KH
2022-05-03 15:04 ` Miklos Szeredi
2022-05-03 15:14 ` Amir Goldstein
2022-05-03 16:54 ` Greg KH
2022-05-03 22:43 ` Dave Chinner
2022-05-04 7:18 ` Miklos Szeredi
2022-05-04 14:22 ` Amir Goldstein
2022-05-05 12:30 ` Karel Zak
2022-05-05 13:59 ` Miklos Szeredi
2022-05-05 23:38 ` tytso
2022-05-06 0:06 ` Amir Goldstein
2022-05-07 0:32 ` Dave Chinner
2022-05-09 12:48 ` Christian Brauner
2022-05-09 14:20 ` Amir Goldstein
2022-05-09 15:08 ` Christian Brauner
2022-05-09 17:07 ` Amir Goldstein
2022-05-09 21:42 ` Vivek Goyal
2022-05-10 3:34 ` Ian Kent
2022-05-10 0:55 ` Dave Chinner
2022-05-10 12:40 ` Christian Brauner
2022-05-11 0:42 ` Dave Chinner
2022-05-11 9:16 ` Christian Brauner
2022-05-10 12:45 ` Florian Weimer
2022-05-10 23:04 ` Dave Chinner
2022-05-10 3:49 ` Miklos Szeredi
2022-05-10 4:27 ` Ian Kent
2022-05-10 8:06 ` Miklos Szeredi
2022-05-10 8:07 ` Miklos Szeredi
2022-05-10 11:53 ` Christian Brauner
2022-05-10 13:15 ` Miklos Szeredi
2022-05-10 13:18 ` Miklos Szeredi
2022-05-10 14:19 ` Christian Brauner
2022-05-10 14:41 ` Miklos Szeredi
2022-05-10 15:30 ` Christian Brauner
2022-05-10 15:47 ` Miklos Szeredi
2022-05-10 15:53 ` Christian Brauner
2022-05-10 12:35 ` Karel Zak [this message]
2022-05-10 23:25 ` Dave Chinner
2022-05-11 8:58 ` Karel Zak
2022-11-14 9:00 ` Abel Wu
2022-11-14 12:35 ` Miklos Szeredi
2022-11-15 3:39 ` Abel Wu
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