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Date: Fri, 4 Apr 2008 12:06:23 -0400
From: Mathieu Desnoyers <compudj@...stal.dyndns.org>
To: Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Cc: LKML <linux-kernel@...r.kernel.org>,
Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] relay: add buffer-only functionality, allowing for
early kernel tracing
* Eduard - Gabriel Munteanu (eduard.munteanu@...ux360.ro) 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.
>
I like this :) But could we trace event sooner if we did not depend on
vmalloc to allocate the buffers ?
I am thinking of receiving a kernel parameter that would reserve a
buffer in the linear kernel mapping (kmalloc ?), or to compile-in a
static buffer, which could be used by relay instead of the vmalloc'd
buffer. That would permit to trace the memory allocator and some other
very early stuff. Basically, relay would have it's "memory pool" to
manage and would do its allocations from this fixed buffer. No free
would be required.
Mathieu
> 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
> +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 6cd8c44..ca9ee3f 100644
> --- a/include/linux/relay.h
> +++ b/include/linux/relay.h
> @@ -68,6 +68,7 @@ struct rchan
> int is_global; /* One global buffer ? */
> struct list_head list; /* for channel list */
> struct dentry *parent; /* parent dentry passed to open */
> + int has_base_filename; /* has a filename associated? */
> char base_filename[NAME_MAX]; /* saved base filename */
> };
>
> @@ -169,6 +170,9 @@ struct rchan *relay_open(const char *base_filename,
> size_t n_subbufs,
> 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 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;
> + 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;
>
> 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;
> }
> @@ -508,8 +523,8 @@ static int __cpuinit relay_hotcpu_callback(struct notifier_block *nb,
>
> /**
> * relay_open - create a new relay channel
> - * @base_filename: base name of files to create
> - * @parent: dentry of parent directory, %NULL for root directory
> + * @base_filename: base name of files to create, %NULL for buffering only
> + * @parent: dentry of parent directory, %NULL for root directory or buffer
> * @subbuf_size: size of sub-buffers
> * @n_subbufs: number of sub-buffers
> * @cb: client callback functions
> @@ -531,8 +546,6 @@ struct rchan *relay_open(const char *base_filename,
> {
> unsigned int i;
> struct rchan *chan;
> - if (!base_filename)
> - return NULL;
>
> if (!(subbuf_size && n_subbufs))
> return NULL;
> @@ -547,12 +560,17 @@ struct rchan *relay_open(const char *base_filename,
> chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
> chan->parent = parent;
> chan->private_data = private_data;
> - strlcpy(chan->base_filename, base_filename, NAME_MAX);
> + if (base_filename) {
> + chan->has_base_filename = 1;
> + strlcpy(chan->base_filename, base_filename, NAME_MAX);
> + } else {
> + chan->has_base_filename = 0;
> + }
> setup_callbacks(chan, cb);
> kref_init(&chan->kref);
>
> mutex_lock(&relay_channels_mutex);
> - for_each_online_cpu(i) {
> + for_each_present_cpu(i) {
> chan->buf[i] = relay_open_buf(chan, i);
> if (!chan->buf[i])
> goto free_bufs;
> @@ -563,7 +581,7 @@ struct rchan *relay_open(const char *base_filename,
> return chan;
>
> free_bufs:
> - for_each_online_cpu(i) {
> + for_each_present_cpu(i) {
> if (!chan->buf[i])
> break;
> relay_close_buf(chan->buf[i]);
> @@ -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.
> + *
> + * 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
> --
> 1.5.2.5
>
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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