From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
LKML <linux-kernel@vger.kernel.org>,
Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Christian Brauner <brauner@kernel.org>,
linux-fsdevel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jonathan Corbet <corbet@lwn.net>,
linux-doc@vger.kernel.org
Subject: Re: [PATCH] tracefs/eventfs: Use root and instance inodes as default ownership
Date: Thu, 4 Jan 2024 11:35:37 -0800 [thread overview]
Message-ID: <CAHk-=wgxhmMcVGvyxTxvjeBaenOmG8t_Erahj16-68whbvh-Ug@mail.gmail.com> (raw)
In-Reply-To: <20240104141517.0657b9d1@gandalf.local.home>
On Thu, 4 Jan 2024 at 11:14, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> "file descriptor" - is just what maps to a specific inode.
Nope. Technically and traditionally, file descriptor is just the
integer index that is used to look up a 'struct file *'.
Except in the kernel, we really just tend to use that term (well, I
do) for the 'struct file *' itself, since the integer 'fd' is usually
not really relevant except at the system call interface.
Which is *NOT* the inode, because the 'struct file' has other things
in it (the file position, the permissions that were used at open time
etc, close-on-exec state etc etc).
> "file description" - is how the file is accessed (position in the file and
> flags associated to how it was opened)
That's a horrible term that shouldn't be used at all. Apparently some
people use it for what is our 'struct file *", also known as a "file
table entry". Avoid it.
If anything, just use "fd" for the integer representation, and "file"
for the pointer to a 'struct file".
But most of the time the two are conceptually interchangeable, in that
an 'fd' just translates directly to a 'struct file *'.
Note that while there's that conceptual direct translation, there's
also very much a "time of use" issue, in that a "fd -> file"
translation happens at one particular time and in one particular user
context, and then it's *done* (so closing and possibly re-using the fd
after it's been looked up does not actually affect an existing 'struct
file *').
And while 'fd -> file' lookup is quick and common, the other way
doesn't exist, because multiple 'fd's can map to one 'struct file *'
thanks to dup() (and 'fork()', since a 'fd -> file' translation always
happens within the context of a particular user space, an 'fd' in one
process is obviously not the same as an 'fd' in another one).
Linus
next prev parent reply other threads:[~2024-01-04 19:35 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-04 1:32 [PATCH] tracefs/eventfs: Use root and instance inodes as default ownership Steven Rostedt
2024-01-04 1:48 ` Al Viro
2024-01-04 2:25 ` Steven Rostedt
2024-01-04 4:39 ` Al Viro
2024-01-04 15:05 ` Steven Rostedt
2024-01-04 18:25 ` Al Viro
2024-01-04 19:10 ` Steven Rostedt
2024-01-04 19:21 ` Linus Torvalds
2024-01-04 19:15 ` Steven Rostedt
2024-01-04 19:26 ` Matthew Wilcox
2024-01-04 19:35 ` Linus Torvalds [this message]
2024-01-04 20:02 ` Linus Torvalds
2024-01-04 21:28 ` Al Viro
2024-01-04 19:03 ` Matthew Wilcox
2024-01-04 1:59 ` Al Viro
2024-01-04 2:17 ` Steven Rostedt
2024-01-05 14:26 ` Christian Brauner
2024-01-05 14:59 ` Steven Rostedt
2024-01-07 12:42 ` Christian Brauner
2024-01-07 17:42 ` Christian Brauner
2024-01-07 18:01 ` Christian Brauner
2024-01-07 18:29 ` Steven Rostedt
2024-01-07 18:32 ` Steven Rostedt
2024-01-08 11:32 ` Christian Brauner
2024-01-08 15:41 ` Steven Rostedt
2024-01-08 11:04 ` Christian Brauner
2024-01-08 15:23 ` Steven Rostedt
2024-01-10 11:45 ` Christian Brauner
2024-01-10 13:07 ` Steven Rostedt
2024-01-10 15:52 ` Steven Rostedt
2024-01-10 16:04 ` Steven Rostedt
2024-01-10 18:31 ` Steven Rostedt
2024-01-11 21:01 ` Christian Brauner
2024-01-11 21:53 ` Steven Rostedt
2024-01-12 8:27 ` Christian Brauner
2024-01-12 13:53 ` Steven Rostedt
2024-01-12 14:22 ` Steven Rostedt
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