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Date: Sun, 6 Apr 2008 20:34:26 +0300
From: Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
To: Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc: Pekka Enberg <penberg@...helsinki.fi>,
LKML <linux-kernel@...r.kernel.org>,
Randy Dunlap <randy.dunlap@...cle.com>,
Tom Zanussi <zanussi@...cast.net>
Subject: [PATCH] relay: add buffer-only functionality, for early kernel
tracing
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. This currently works for
tracing just after kmem_init_cache() runs, no earlier.
Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
---
Documentation/filesystems/relay.txt | 11 ++++
include/linux/relay.h | 5 ++
kernel/relay.c | 113 ++++++++++++++++++++++++++---------
3 files changed, 101 insertions(+), 28 deletions(-)
diff --git a/Documentation/filesystems/relay.txt b/Documentation/filesystems/relay.txt
index 094f2d2..b417f83 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 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..953fc05 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -48,6 +48,7 @@ struct rchan_buf
size_t *padding; /* padding counts per sub-buffer */
size_t prev_padding; /* temporary variable */
size_t bytes_consumed; /* bytes consumed in cur read subbuf */
+ size_t early_bytes; /* bytes consumed before VFS inited */
unsigned int cpu; /* this buf's cpu */
} ____cacheline_aligned;
@@ -68,6 +69,7 @@ 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 +171,9 @@ 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..c1f36f4 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);
+
+ kfree(tmpname);
+
+ if (!dentry)
+ goto failed;
+ buf->dentry = dentry;
+
+ return 0;
+
+failed:
+ return 1;
+}
+
/*
* relay_open_buf - create a new relay channel buffer
*
@@ -386,44 +415,31 @@ 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 +524,8 @@ 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 +547,6 @@ 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 +561,15 @@ 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);
+ }
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 +580,7 @@ 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 +593,41 @@ 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 if 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);
+ chan->buf[i]->dentry->d_inode->i_size =
+ chan->buf[i]->early_bytes;
+ }
+ mutex_unlock(&relay_channels_mutex);
+
+ return 0;
+}
+
+/**
* relay_switch_subbuf - switch to a new sub-buffer
* @buf: channel buffer
* @length: size of current event
@@ -598,8 +650,13 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
buf->padding[old_subbuf] = buf->prev_padding;
buf->subbufs_produced++;
- buf->dentry->d_inode->i_size += buf->chan->subbuf_size -
- buf->padding[old_subbuf];
+ if (buf->dentry)
+ buf->dentry->d_inode->i_size +=
+ buf->chan->subbuf_size -
+ buf->padding[old_subbuf];
+ else
+ buf->early_bytes += buf->chan->subbuf_size -
+ buf->padding[old_subbuf];
smp_mb();
if (waitqueue_active(&buf->read_wait))
/*
--
1.5.2.5
--
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