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Message-Id: <20250420140758.601ae8abaa03aacb33ce7084@linux-foundation.org>
Date: Sun, 20 Apr 2025 14:07:58 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: linux@...blig.org
Cc: andriy.shevchenko@...ux.intel.com, viro@...iv.linux.org.uk,
corbet@....net, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] relay: Remove unused relay_late_setup_files
On Sat, 19 Apr 2025 00:49:32 +0100 linux@...blig.org wrote:
> From: "Dr. David Alan Gilbert" <linux@...blig.org>
>
> The last use of relay_late_setup_files() was removed in 2018
> by commit 2b47733045aa ("drm/i915/guc: Merge log relay file and channel
> creation")
>
> Remove it and the helper it used.
>
> relay_late_setup_files() was used for eventually registering
> 'buffer only' channels. With it gone, delete the docs that
> explain how to do that. Which suggests it should be possible
> to lose the 'has_base_filename' flags.
>
> (Are there any other uses??)
>
For some reason get_maintainer points at Al and Andy for relay.c but my
mental rolodex thinks "Axboe".
Jens, does this look OK?
> ---
> Documentation/filesystems/relay.rst | 10 ---
> include/linux/relay.h | 3 -
> kernel/relay.c | 111 +---------------------------
> 3 files changed, 1 insertion(+), 123 deletions(-)
>
> diff --git a/Documentation/filesystems/relay.rst b/Documentation/filesystems/relay.rst
> index 04ad083cfe62..292ba8492aeb 100644
> --- a/Documentation/filesystems/relay.rst
> +++ b/Documentation/filesystems/relay.rst
> @@ -301,16 +301,6 @@ user-defined data with a channel, and is immediately available
> (including in create_buf_file()) via chan->private_data or
> buf->chan->private_data.
>
> -Buffer-only channels
> ---------------------
> -
> -These channels have no files associated and can be created with
> -relay_open(NULL, NULL, ...). Such channels are useful in scenarios such
> -as when doing early tracing in the kernel, before the VFS is up. In these
> -cases, one may open a buffer-only channel and then call
> -relay_late_setup_files() when the kernel is ready to handle files,
> -to expose the buffered data to the userspace.
> -
> Channel 'modes'
> ---------------
>
> diff --git a/include/linux/relay.h b/include/linux/relay.h
> index 72b876dd5cb8..b3224111d074 100644
> --- a/include/linux/relay.h
> +++ b/include/linux/relay.h
> @@ -159,9 +159,6 @@ struct rchan *relay_open(const char *base_filename,
> size_t n_subbufs,
> const struct rchan_callbacks *cb,
> void *private_data);
> -extern int relay_late_setup_files(struct rchan *chan,
> - const char *base_filename,
> - struct dentry *parent);
> extern void relay_close(struct rchan *chan);
> extern void relay_flush(struct rchan *chan);
> extern void relay_subbufs_consumed(struct rchan *chan,
> diff --git a/kernel/relay.c b/kernel/relay.c
> index 5ac7e711e4b6..c0c93a04d4ce 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -452,7 +452,7 @@ int relay_prepare_cpu(unsigned int cpu)
>
> /**
> * relay_open - create a new relay channel
> - * @base_filename: base name of files to create, %NULL for buffering only
> + * @base_filename: base name of files to create
> * @parent: dentry of parent directory, %NULL for root directory or buffer
> * @subbuf_size: size of sub-buffers
> * @n_subbufs: number of sub-buffers
> @@ -465,10 +465,6 @@ int relay_prepare_cpu(unsigned int cpu)
> * attributes specified. The created channel buffer files
> * will be named base_filename0...base_filenameN-1. File
> * permissions will be %S_IRUSR.
> - *
> - * If opening a buffer (@parent = NULL) that you later wish to register
> - * in a filesystem, call relay_late_setup_files() once the @parent dentry
> - * is available.
> */
> struct rchan *relay_open(const char *base_filename,
> struct dentry *parent,
> @@ -540,111 +536,6 @@ struct rchan_percpu_buf_dispatcher {
> struct dentry *dentry;
> };
>
> -/* Called in atomic context. */
> -static void __relay_set_buf_dentry(void *info)
> -{
> - struct rchan_percpu_buf_dispatcher *p = info;
> -
> - relay_set_buf_dentry(p->buf, p->dentry);
> -}
> -
> -/**
> - * relay_late_setup_files - triggers file creation
> - * @chan: channel to operate on
> - * @base_filename: base name of files to create
> - * @parent: dentry of parent directory, %NULL for root directory
> - *
> - * Returns 0 if successful, non-zero otherwise.
> - *
> - * Use to setup files for a previously buffer-only channel created
> - * by relay_open() with a NULL parent dentry.
> - *
> - * For example, this is useful for perfomring early tracing in kernel,
> - * before VFS is up and then exposing the early results once the dentry
> - * is available.
> - */
> -int relay_late_setup_files(struct rchan *chan,
> - const char *base_filename,
> - struct dentry *parent)
> -{
> - int err = 0;
> - unsigned int i, curr_cpu;
> - unsigned long flags;
> - struct dentry *dentry;
> - struct rchan_buf *buf;
> - struct rchan_percpu_buf_dispatcher disp;
> -
> - if (!chan || !base_filename)
> - return -EINVAL;
> -
> - strscpy(chan->base_filename, base_filename, NAME_MAX);
> -
> - mutex_lock(&relay_channels_mutex);
> - /* Is chan already set up? */
> - if (unlikely(chan->has_base_filename)) {
> - mutex_unlock(&relay_channels_mutex);
> - return -EEXIST;
> - }
> - chan->has_base_filename = 1;
> - chan->parent = parent;
> -
> - if (chan->is_global) {
> - err = -EINVAL;
> - buf = *per_cpu_ptr(chan->buf, 0);
> - if (!WARN_ON_ONCE(!buf)) {
> - dentry = relay_create_buf_file(chan, buf, 0);
> - if (dentry && !WARN_ON_ONCE(!chan->is_global)) {
> - relay_set_buf_dentry(buf, dentry);
> - err = 0;
> - }
> - }
> - mutex_unlock(&relay_channels_mutex);
> - return err;
> - }
> -
> - curr_cpu = get_cpu();
> - /*
> - * The CPU hotplug notifier ran before us and created buffers with
> - * no files associated. So it's safe to call relay_setup_buf_file()
> - * on all currently online CPUs.
> - */
> - for_each_online_cpu(i) {
> - buf = *per_cpu_ptr(chan->buf, i);
> - if (unlikely(!buf)) {
> - WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
> - err = -EINVAL;
> - break;
> - }
> -
> - dentry = relay_create_buf_file(chan, buf, i);
> - if (unlikely(!dentry)) {
> - err = -EINVAL;
> - break;
> - }
> -
> - if (curr_cpu == i) {
> - local_irq_save(flags);
> - relay_set_buf_dentry(buf, dentry);
> - local_irq_restore(flags);
> - } else {
> - disp.buf = buf;
> - disp.dentry = dentry;
> - smp_mb();
> - /* relay_channels_mutex must be held, so wait. */
> - err = smp_call_function_single(i,
> - __relay_set_buf_dentry,
> - &disp, 1);
> - }
> - if (unlikely(err))
> - break;
> - }
> - put_cpu();
> - mutex_unlock(&relay_channels_mutex);
> -
> - return err;
> -}
> -EXPORT_SYMBOL_GPL(relay_late_setup_files);
> -
> /**
> * relay_switch_subbuf - switch to a new sub-buffer
> * @buf: channel buffer
> --
> 2.49.0
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