On Tue, Jan 16, 2024 at 05:55:32PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rost...@goodmis.org>
>
> The dentries and inodes are created in the readdir for the sole purpose of
> getting a consistent inode number. Linus stated that is unnecessary, and
> that all inodes can have the same inode number. For a virtual file system
> they are pretty meaningless.
>
> Instead use a single unique inode number for all files and one for all
> directories.
>
> Link: https://lore.kernel.org/all/20240116133753.2808d...@gandalf.local.home/
> Link:
> https://lore.kernel.org/linux-trace-kernel/20240116211353.412180...@goodmis.org
>
> Cc: Masami Hiramatsu <mhira...@kernel.org>
> Cc: Mark Rutland <mark.rutl...@arm.com>
> Cc: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
> Cc: Christian Brauner <brau...@kernel.org>
> Cc: Al Viro <v...@zeniv.linux.org.uk>
> Cc: Ajay Kaher <ajay.ka...@broadcom.com>
> Suggested-by: Linus Torvalds <torva...@linux-foundation.org>
> Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org>
> ---
> fs/tracefs/event_inode.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
> index fdff53d5a1f8..5edf0b96758b 100644
> --- a/fs/tracefs/event_inode.c
> +++ b/fs/tracefs/event_inode.c
> @@ -32,6 +32,10 @@
> */
> static DEFINE_MUTEX(eventfs_mutex);
>
> +/* Choose something "unique" ;-) */
> +#define EVENTFS_FILE_INODE_INO 0x12c4e37
> +#define EVENTFS_DIR_INODE_INO 0x134b2f5
> +
> /*
> * The eventfs_inode (ei) itself is protected by SRCU. It is released from
> * its parent's list and will have is_freed set (under eventfs_mutex).
> @@ -352,6 +356,9 @@ static struct dentry *create_file(const char *name,
> umode_t mode,
> inode->i_fop = fop;
> inode->i_private = data;
>
> + /* All files will have the same inode number */
> + inode->i_ino = EVENTFS_FILE_INODE_INO;
> +
> ti = get_tracefs(inode);
> ti->flags |= TRACEFS_EVENT_INODE;
> d_instantiate(dentry, inode);
> @@ -388,6 +395,9 @@ static struct dentry *create_dir(struct eventfs_inode
> *ei, struct dentry *parent
> inode->i_op = &eventfs_root_dir_inode_operations;
> inode->i_fop = &eventfs_file_operations;
>
> + /* All directories will have the same inode number */
> + inode->i_ino = EVENTFS_DIR_INODE_INO;
Regrettably, this leads to find failing on 6.8-rc1 (see xfs/55[89] in
fstests):
# find /sys/kernel/debug/tracing/ >/dev/null
find: File system loop detected;
‘/sys/kernel/debug/tracing/events/initcall/initcall_finish’ is part of the same
file system loop as ‘/sys/kernel/debug/tracing/events/initcall’.
find: File system loop detected;
‘/sys/kernel/debug/tracing/events/initcall/initcall_start’ is part of the same
file system loop as ‘/sys/kernel/debug/tracing/events/initcall’.
find: File system loop detected;
‘/sys/kernel/debug/tracing/events/initcall/initcall_level’ is part of the same
file system loop as ‘/sys/kernel/debug/tracing/events/initcall’.
There were no such reports on 6.7.0; AFAICT find(1) is tripping over
parent and child subdirectory having the same dev/i_ino. Changing this
line to the following:
/* All directories will NOT have the same inode number */
inode->i_ino = (unsigned long)inode;
makes the messages about filesystem loops go away, though I don't think
leaking raw kernel pointers is an awesome idea.
--D
> +
> ti = get_tracefs(inode);
> ti->flags |= TRACEFS_EVENT_INODE;
>
> --
> 2.43.0
>
>
>
