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Date: Fri, 4 Apr 2008 09:08:01 -0700
From: Randy Dunlap <randy.dunlap@...cle.com>
To: Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Cc: Mathieu Desnoyers <compudj@...stal.dyndns.org>,
LKML <linux-kernel@...r.kernel.org>,
Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] relay: add buffer-only functionality, allowing for
early kernel tracing
On Fri, 4 Apr 2008 18:33:03 +0300 Eduard - Gabriel Munteanu wrote:
> relay_open() can now handle NULL base_filename, to register a
> buffer-only channel. Using a new function, relay_late_setup_files(), one
> can assign files after creating the channel, thus allowing for doing
> early tracing in the kernel, before VFS is up.
>
> Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
> ---
> Documentation/filesystems/relay.txt | 11 ++++
> include/linux/relay.h | 4 ++
> kernel/relay.c | 102 ++++++++++++++++++++++++++---------
> 3 files changed, 91 insertions(+), 26 deletions(-)
>
> diff --git a/Documentation/filesystems/relay.txt b/Documentation/filesystems/relay.txt
> index 094f2d2..b59c228 100644
> --- a/Documentation/filesystems/relay.txt
> +++ b/Documentation/filesystems/relay.txt
> @@ -161,6 +161,7 @@ TBD(curr. line MT:/API/)
> relay_close(chan)
> relay_flush(chan)
> relay_reset(chan)
> + relay_late_setup_files(chan, base_filename, parent)
>
> channel management typically called on instigation of userspace:
>
> @@ -294,6 +295,16 @@ 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 channel a buffer-only channel and then call
~~~~~~~~~
d/a channel/
> +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/kernel/relay.c b/kernel/relay.c
> index 4c035a8..4bea94a 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -378,6 +378,35 @@ void relay_reset(struct rchan *chan)
> }
> EXPORT_SYMBOL_GPL(relay_reset);
>
> +static int relay_setup_buf_file(struct rchan *chan,
> + struct rchan_buf *buf,
> + unsigned int cpu)
> +{
> + struct dentry *dentry;
> + char *tmpname;
> +
> + tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
> + if (!tmpname)
> + goto failed;
> + snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
> +
> + /* Create file in fs */
> + dentry = chan->cb->create_buf_file(tmpname, chan->parent,
> + S_IRUSR, buf,
> + &chan->is_global);
> +
> + if (!dentry)
> + goto failed;
above leaks tmpname ?
> + buf->dentry = dentry;
> +
> + kfree(tmpname);
> +
> + return 0;
> +
> +failed:
> + return 1;
> +}
> +
> /*
> * relay_open_buf - create a new relay channel buffer
> *
> @@ -386,44 +415,30 @@ EXPORT_SYMBOL_GPL(relay_reset);
> static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
> {
> struct rchan_buf *buf = NULL;
> - struct dentry *dentry;
> - char *tmpname;
>
> if (chan->is_global)
> return chan->buf[0];
>
> - tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
> - if (!tmpname)
> - goto end;
> - snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
> -
> buf = relay_create_buf(chan);
> if (!buf)
> - goto free_name;
> + goto end;
> +
> + if (chan->has_base_filename)
> + if (relay_setup_buf_file(chan, buf, cpu)) goto free_buf;
Put 'goto free_buf;' on separate line.
>
> buf->cpu = cpu;
> __relay_reset(buf, 1);
>
> - /* Create file in fs */
> - dentry = chan->cb->create_buf_file(tmpname, chan->parent, S_IRUSR,
> - buf, &chan->is_global);
> - if (!dentry)
> - goto free_buf;
> -
> - buf->dentry = dentry;
> -
> if(chan->is_global) {
> chan->buf[0] = buf;
> buf->cpu = 0;
> }
>
> - goto free_name;
> + goto end;
>
> free_buf:
> relay_destroy_buf(buf);
> buf = NULL;
> -free_name:
> - kfree(tmpname);
> end:
> return buf;
> }
> @@ -576,6 +594,38 @@ free_bufs:
> EXPORT_SYMBOL_GPL(relay_open);
>
> /**
> + * 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 is successful, non-zero otherwise.
s/is/if/
> + *
> + * Use to setup files for a previously buffer-only channel.
> + * Useful to do early tracing in kernel, before VFS is up, for example.
> + */
> +int relay_late_setup_files(struct rchan *chan,
> + const char *base_filename,
> + struct dentry *parent)
> +{
> + unsigned int i;
> +
> + if (!chan || !base_filename)
> + return 1;
> +
> + strlcpy(chan->base_filename, base_filename, NAME_MAX);
> + chan->has_base_filename = 1;
> + chan->parent = parent;
> +
> + mutex_lock(&relay_channels_mutex);
> + for_each_present_cpu(i)
> + relay_setup_buf_file(chan, chan->buf[i], i);
> + mutex_unlock(&relay_channels_mutex);
> +
> + return 0;
> +}
> +
> +/**
> * relay_switch_subbuf - switch to a new sub-buffer
> * @buf: channel buffer
> * @length: size of current event
---
~Randy
--
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