From: Al Viro <viro@zeniv.linux.org.uk> To: Linus Torvalds <torvalds@linux-foundation.org> Cc: Christian Brauner <christian@brauner.io>, Andy Lutomirski <luto@amacapital.net>, Daniel Colascione <dancol@google.com>, Jann Horn <jannh@google.com>, Andrew Lutomirski <luto@kernel.org>, David Howells <dhowells@redhat.com>, "Serge E. Hallyn" <serge@hallyn.com>, Linux API <linux-api@vger.kernel.org>, Linux List Kernel Mailing <linux-kernel@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, "Eric W. Biederman" <ebiederm@xmission.com>, Konstantin Khlebnikov <khlebnikov@yandex-team.ru>, Kees Cook <keescook@chromium.org>, Alexey Dobriyan <adobriyan@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Michael Kerrisk-manpages <mtk.manpages@gmail.com>, Jonathan Kowalski <bl0pbl33p@gmail.com>, "Dmitry V. Levin" <ldv@altlinux.org>, Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>, Aleksa Sarai <cyphar@cyphar.com>, Joel Fernandes <joel@joelfernandes.org> Subject: Re: [PATCH v2 0/5] pid: add pidfd_open() Date: Mon, 1 Apr 2019 01:09:37 +0100 [thread overview] Message-ID: <20190401000937.GG2217@ZenIV.linux.org.uk> (raw) In-Reply-To: <CAHk-=whw1cnWPSWw1tHXT5xTMbnJFbCtx9_re6U1RZ_7LE9gXA@mail.gmail.com> On Sun, Mar 31, 2019 at 04:40:15PM -0700, Linus Torvalds wrote: > The clever alternative, which might be the RightWay(tm) is to just > create a completely unattached dentry, and basically tie it into the > actual /proc filesystem hierarchy at lookup() time when somebody does > the openat() using it for the first time. You'd get a very simple > callback: since the dentry would be unattached, you'd be guaranteed to > get a "lookup()" from the VFS layer, and that lookup would then do the > "hook into the actual /proc filesystem". Ugh... Which vfsmount would you have to go with it? > We already kind of do things like that in the VFS layer when we have > unattached dentries (because of "look up by filehandle" etc). In many > ways the "pidfd_open()" really is exactly a "look up by file handle" > operation, it just so happens that the "file handle" is just the > pid/namespace combination. Except that we never let unattached _directory_ dentries out - if we can't reattach them to the tree, open-by-handle will tell you to take a hike. > And if the splice alias (which is what the VFS layer calls that "tie > aliased dentry to the parent" operation) fails, because the /proc > filesystem isn't mounted or whatever, then trying to look up names off > the thing will also fail. > It's a tiny bit too clever for my taste, and it's not *exactly* the > same thing as our normal inode alias handling, but it's pretty close > conceptually (and even practically). It's more than a tiny bit too clever for mine... > So it would basically do something very similar to the ioctl, but it > would do it implicitly and automatically at that first lookup. > > That would also mean that you'd not actually pay the cost of doing any > of this *unless* you also end up trying to open things in /proc using > that pidfd. Al, back to normal life and digging through several flamefests from hell...
WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@zeniv.linux.org.uk> To: Linus Torvalds <torvalds@linux-foundation.org> Cc: Christian Brauner <christian@brauner.io>, Andy Lutomirski <luto@amacapital.net>, Daniel Colascione <dancol@google.com>, Jann Horn <jannh@google.com>, Andrew Lutomirski <luto@kernel.org>, David Howells <dhowells@redhat.com>, "Serge E. Hallyn" <serge@hallyn.com>, Linux API <linux-api@vger.kernel.org>, Linux List Kernel Mailing <linux-kernel@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, "Eric W. Biederman" <ebiederm@xmission.com>, Konstantin Khlebnikov <khlebnikov@yandex-team.ru>, Kees Cook <keescook@chromium.org>, Alexey Dobriyan <adobriyan@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Michael Kerrisk-manpages <mtk.manpages@gmail.com>, Jonathan Kowalski <bl0pbl33p@gmail.com>, "Dmitry V. Levin" <ldv@altlinux.org>, Andrew Morton <akpm@linu> Subject: Re: [PATCH v2 0/5] pid: add pidfd_open() Date: Mon, 1 Apr 2019 01:09:37 +0100 [thread overview] Message-ID: <20190401000937.GG2217@ZenIV.linux.org.uk> (raw) In-Reply-To: <CAHk-=whw1cnWPSWw1tHXT5xTMbnJFbCtx9_re6U1RZ_7LE9gXA@mail.gmail.com> On Sun, Mar 31, 2019 at 04:40:15PM -0700, Linus Torvalds wrote: > The clever alternative, which might be the RightWay(tm) is to just > create a completely unattached dentry, and basically tie it into the > actual /proc filesystem hierarchy at lookup() time when somebody does > the openat() using it for the first time. You'd get a very simple > callback: since the dentry would be unattached, you'd be guaranteed to > get a "lookup()" from the VFS layer, and that lookup would then do the > "hook into the actual /proc filesystem". Ugh... Which vfsmount would you have to go with it? > We already kind of do things like that in the VFS layer when we have > unattached dentries (because of "look up by filehandle" etc). In many > ways the "pidfd_open()" really is exactly a "look up by file handle" > operation, it just so happens that the "file handle" is just the > pid/namespace combination. Except that we never let unattached _directory_ dentries out - if we can't reattach them to the tree, open-by-handle will tell you to take a hike. > And if the splice alias (which is what the VFS layer calls that "tie > aliased dentry to the parent" operation) fails, because the /proc > filesystem isn't mounted or whatever, then trying to look up names off > the thing will also fail. > It's a tiny bit too clever for my taste, and it's not *exactly* the > same thing as our normal inode alias handling, but it's pretty close > conceptually (and even practically). It's more than a tiny bit too clever for mine... > So it would basically do something very similar to the ioctl, but it > would do it implicitly and automatically at that first lookup. > > That would also mean that you'd not actually pay the cost of doing any > of this *unless* you also end up trying to open things in /proc using > that pidfd. Al, back to normal life and digging through several flamefests from hell...
next prev parent reply other threads:[~2019-04-01 0:09 UTC|newest] Thread overview: 158+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-03-29 15:54 [PATCH v2 0/5] pid: add pidfd_open() Christian Brauner 2019-03-29 15:54 ` [PATCH v2 1/5] Make anon_inodes unconditional Christian Brauner 2019-03-29 15:54 ` [PATCH v2 2/5] pid: add pidfd_open() Christian Brauner 2019-03-29 23:45 ` Jann Horn 2019-03-29 23:45 ` Jann Horn 2019-03-29 23:55 ` Christian Brauner 2019-03-29 23:55 ` Christian Brauner 2019-03-30 11:53 ` Jürg Billeter 2019-03-30 14:37 ` Christian Brauner 2019-03-30 14:51 ` Jonathan Kowalski 2019-03-30 14:51 ` Jonathan Kowalski 2019-03-29 15:54 ` [PATCH v2 3/5] signal: support pidfd_open() with pidfd_send_signal() Christian Brauner 2019-03-29 15:54 ` [PATCH v2 4/5] signal: PIDFD_SIGNAL_TID threads via pidfds Christian Brauner 2019-03-30 1:06 ` Jann Horn 2019-03-30 1:06 ` Jann Horn 2019-03-30 1:22 ` Christian Brauner 2019-03-30 1:22 ` Christian Brauner 2019-03-30 1:34 ` Christian Brauner 2019-03-30 1:34 ` Christian Brauner 2019-03-30 1:42 ` Christian Brauner 2019-03-30 1:42 ` Christian Brauner 2019-03-29 15:54 ` [PATCH v2 5/5] tests: add pidfd_open() tests Christian Brauner 2019-03-30 16:09 ` [PATCH v2 0/5] pid: add pidfd_open() Linus Torvalds 2019-03-30 16:09 ` Linus Torvalds 2019-03-30 16:11 ` Daniel Colascione 2019-03-30 16:11 ` Daniel Colascione 2019-03-30 16:16 ` Linus Torvalds 2019-03-30 16:16 ` Linus Torvalds 2019-03-30 16:18 ` Linus Torvalds 2019-03-30 16:18 ` Linus Torvalds 2019-03-31 1:07 ` Joel Fernandes 2019-03-31 1:07 ` Joel Fernandes 2019-03-31 2:34 ` Jann Horn 2019-03-31 2:34 ` Jann Horn 2019-03-31 4:08 ` Joel Fernandes 2019-03-31 4:08 ` Joel Fernandes 2019-03-31 4:46 ` Jann Horn 2019-03-31 4:46 ` Jann Horn 2019-03-31 14:52 ` Linus Torvalds 2019-03-31 14:52 ` Linus Torvalds 2019-03-31 15:05 ` Christian Brauner 2019-03-31 15:05 ` Christian Brauner 2019-03-31 15:21 ` Daniel Colascione 2019-03-31 15:21 ` Daniel Colascione 2019-03-31 15:33 ` Jonathan Kowalski 2019-03-31 15:33 ` Jonathan Kowalski 2019-03-30 16:19 ` Christian Brauner 2019-03-30 16:19 ` Christian Brauner 2019-03-30 16:24 ` Linus Torvalds 2019-03-30 16:24 ` Linus Torvalds 2019-03-30 16:34 ` Daniel Colascione 2019-03-30 16:34 ` Daniel Colascione 2019-03-30 16:38 ` Christian Brauner 2019-03-30 16:38 ` Christian Brauner 2019-03-30 17:04 ` Linus Torvalds 2019-03-30 17:04 ` Linus Torvalds 2019-03-30 17:12 ` Christian Brauner 2019-03-30 17:12 ` Christian Brauner 2019-03-30 17:24 ` Linus Torvalds 2019-03-30 17:24 ` Linus Torvalds 2019-03-30 17:37 ` Christian Brauner 2019-03-30 17:37 ` Christian Brauner 2019-03-30 17:50 ` Jonathan Kowalski 2019-03-30 17:50 ` Jonathan Kowalski 2019-03-30 17:52 ` Christian Brauner 2019-03-30 17:52 ` Christian Brauner 2019-03-30 17:59 ` Jonathan Kowalski 2019-03-30 17:59 ` Jonathan Kowalski 2019-03-30 18:02 ` Christian Brauner 2019-03-30 18:02 ` Christian Brauner 2019-03-30 18:00 ` Jann Horn 2019-03-30 18:00 ` Jann Horn 2019-03-31 20:09 ` Andy Lutomirski 2019-03-31 20:09 ` Andy Lutomirski 2019-03-31 21:03 ` Linus Torvalds 2019-03-31 21:03 ` Linus Torvalds 2019-03-31 21:10 ` Christian Brauner 2019-03-31 21:10 ` Christian Brauner 2019-03-31 21:17 ` Linus Torvalds 2019-03-31 21:17 ` Linus Torvalds 2019-03-31 22:03 ` Christian Brauner 2019-03-31 22:03 ` Christian Brauner 2019-03-31 22:16 ` Linus Torvalds 2019-03-31 22:16 ` Linus Torvalds 2019-03-31 22:33 ` Christian Brauner 2019-03-31 22:33 ` Christian Brauner 2019-04-01 0:52 ` Jann Horn 2019-04-01 0:52 ` Jann Horn 2019-04-01 8:47 ` Yann Droneaud 2019-04-01 8:47 ` Yann Droneaud 2019-04-01 10:03 ` Jonathan Kowalski 2019-04-01 10:03 ` Jonathan Kowalski 2019-03-31 23:40 ` Linus Torvalds 2019-03-31 23:40 ` Linus Torvalds 2019-04-01 0:09 ` Al Viro [this message] 2019-04-01 0:09 ` Al Viro 2019-04-01 0:18 ` Linus Torvalds 2019-04-01 0:18 ` Linus Torvalds 2019-04-01 0:21 ` Christian Brauner 2019-04-01 0:21 ` Christian Brauner 2019-04-01 6:37 ` Al Viro 2019-04-01 6:37 ` Al Viro 2019-04-01 6:41 ` Al Viro 2019-04-01 6:41 ` Al Viro 2019-03-31 22:03 ` Jonathan Kowalski 2019-03-31 22:03 ` Jonathan Kowalski 2019-04-01 2:13 ` Andy Lutomirski 2019-04-01 2:13 ` Andy Lutomirski 2019-04-01 11:40 ` Aleksa Sarai 2019-04-01 11:40 ` Aleksa Sarai 2019-04-01 15:36 ` Linus Torvalds 2019-04-01 15:36 ` Linus Torvalds 2019-04-01 15:47 ` Christian Brauner 2019-04-01 15:47 ` Christian Brauner 2019-04-01 15:55 ` Daniel Colascione 2019-04-01 15:55 ` Daniel Colascione 2019-04-01 16:01 ` Linus Torvalds 2019-04-01 16:01 ` Linus Torvalds 2019-04-01 16:13 ` Daniel Colascione 2019-04-01 16:13 ` Daniel Colascione 2019-04-01 19:42 ` Christian Brauner 2019-04-01 19:42 ` Christian Brauner 2019-04-01 21:30 ` Linus Torvalds 2019-04-01 21:30 ` Linus Torvalds 2019-04-01 21:58 ` Jonathan Kowalski 2019-04-01 21:58 ` Jonathan Kowalski 2019-04-01 22:13 ` Linus Torvalds 2019-04-01 22:13 ` Linus Torvalds 2019-04-01 22:34 ` Daniel Colascione 2019-04-01 22:34 ` Daniel Colascione 2019-04-01 16:07 ` Jonathan Kowalski 2019-04-01 16:07 ` Jonathan Kowalski 2019-04-01 16:15 ` Linus Torvalds 2019-04-01 16:15 ` Linus Torvalds 2019-04-01 16:27 ` Jonathan Kowalski 2019-04-01 16:27 ` Jonathan Kowalski 2019-04-01 16:21 ` Daniel Colascione 2019-04-01 16:21 ` Daniel Colascione 2019-04-01 16:29 ` Linus Torvalds 2019-04-01 16:29 ` Linus Torvalds 2019-04-01 16:45 ` Daniel Colascione 2019-04-01 16:45 ` Daniel Colascione 2019-04-01 17:00 ` David Laight 2019-04-01 17:00 ` David Laight 2019-04-01 17:32 ` Linus Torvalds 2019-04-01 17:32 ` Linus Torvalds 2019-04-02 11:03 ` Florian Weimer 2019-04-02 11:03 ` Florian Weimer 2019-04-01 16:10 ` Andy Lutomirski 2019-04-01 16:10 ` Andy Lutomirski 2019-04-01 12:04 ` Christian Brauner 2019-04-01 12:04 ` Christian Brauner 2019-04-01 13:43 ` Jann Horn 2019-04-01 13:43 ` Jann Horn 2019-03-31 21:19 ` Christian Brauner 2019-03-31 21:19 ` Christian Brauner 2019-03-30 16:37 ` Christian Brauner 2019-03-30 16:37 ` Christian Brauner
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