Allows one to create and use a channel with no associated files. Files
can be initialized later. This is useful in scenarios such as logging
in early code, before VFS is up. Therefore, such channels can be
created and used as soon as kmem_cache_init() completed.
This is needed by kmemtrace to do tracing in early kernel code.
Signed-off-by: Eduard - Gabriel Munteanu <[email protected]>
---
Documentation/filesystems/relay.txt | 11 +++
include/linux/relay.h | 5 +
kernel/relay.c | 141 +++++++++++++++++++++++++++--------
3 files changed, 126 insertions(+), 31 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 a3a03e7..1d3dcf8 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -49,6 +49,7 @@ 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;
@@ -69,6 +70,7 @@ 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 */
};
@@ -170,6 +172,9 @@ 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 250a27a..80a6a40 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -407,6 +407,39 @@ 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;
+ unsigned long flags;
+ 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;
+ spin_lock_irqsave(&buf->rw_lock, flags);
+ buf->dentry = dentry;
+ buf->dentry->d_inode->i_size = buf->early_bytes;
+ spin_unlock_irqrestore(&buf->rw_lock, flags);
+
+ return 0;
+
+failed:
+ return 1;
+}
+
/*
* relay_open_buf - create a new relay channel buffer
*
@@ -415,48 +448,33 @@ 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;
+ return NULL;
spin_lock_init(&buf->rw_lock);
+ 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;
+ return buf;
free_buf:
relay_destroy_buf(buf);
- buf = NULL;
-free_name:
- kfree(tmpname);
-end:
- return buf;
+ return NULL;
}
/**
@@ -539,8 +557,8 @@ 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
@@ -562,8 +580,6 @@ 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;
@@ -578,7 +594,10 @@ 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);
@@ -607,6 +626,62 @@ 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;
+ int err;
+ struct rchan_buf *buf;
+
+ if (!chan || !base_filename)
+ return 1;
+
+ strlcpy(chan->base_filename, base_filename, NAME_MAX);
+
+ mutex_lock(&relay_channels_mutex);
+ if (unlikely(chan->has_base_filename))
+ goto out;
+ chan->has_base_filename = 1;
+ chan->parent = parent;
+ /*
+ * 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 = chan->buf[i];
+
+ if (unlikely(!buf)) {
+ printk(KERN_ERR "relay_late_setup_files: "
+ "all CPUs should have buffers!\n");
+ goto out;
+ }
+
+ err = relay_setup_buf_file(chan, buf, i);
+ if (unlikely(err))
+ goto out;
+ }
+ mutex_unlock(&relay_channels_mutex);
+
+ return 0;
+
+out:
+ mutex_unlock(&relay_channels_mutex);
+ return 1;
+}
+
+/**
* relay_switch_subbuf - switch to a new sub-buffer
* @buf: channel buffer
* @length: size of current event
@@ -629,8 +704,13 @@ 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))
/*
@@ -1241,9 +1321,8 @@ EXPORT_SYMBOL_GPL(relay_file_operations);
static __init int relay_init(void)
{
-
hotcpu_notifier(relay_hotcpu_callback, 0);
return 0;
}
-module_init(relay_init);
+early_initcall(relay_init);
--
1.5.5.4
* Eduard - Gabriel Munteanu ([email protected]) wrote:
> Allows one to create and use a channel with no associated files. Files
> can be initialized later. This is useful in scenarios such as logging
> in early code, before VFS is up. Therefore, such channels can be
> created and used as soon as kmem_cache_init() completed.
>
> This is needed by kmemtrace to do tracing in early kernel code.
>
> Signed-off-by: Eduard - Gabriel Munteanu <[email protected]>
> ---
> Documentation/filesystems/relay.txt | 11 +++
> include/linux/relay.h | 5 +
> kernel/relay.c | 141 +++++++++++++++++++++++++++--------
> 3 files changed, 126 insertions(+), 31 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 a3a03e7..1d3dcf8 100644
> --- a/include/linux/relay.h
> +++ b/include/linux/relay.h
> @@ -49,6 +49,7 @@ 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;
>
> @@ -69,6 +70,7 @@ 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 */
> };
>
> @@ -170,6 +172,9 @@ 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 250a27a..80a6a40 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -407,6 +407,39 @@ 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;
> + unsigned long flags;
> + 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;
> + spin_lock_irqsave(&buf->rw_lock, flags);
spin_lock_* on a variable named rw_lock, insn't it a bit confusing ?
See rwlock_* and friends to figure out why this naming is not so
appropriate.
> + buf->dentry = dentry;
> + buf->dentry->d_inode->i_size = buf->early_bytes;
> + spin_unlock_irqrestore(&buf->rw_lock, flags);
As long as this rw_lock is not taken on the read/write, etc path, it
won't protect against races. I think it should be left to the
relay_setup_buf_file() caller to provide proper synchronization, and
therefore begs for a comment on top of relay_late_setup_files().
Note that since relay_late_setup_files() takes a mutex, locking will
become a bit problematic, since you cannot nest a spinlock in a mutex.
> +
> + return 0;
> +
> +failed:
> + return 1;
> +}
> +
> /*
> * relay_open_buf - create a new relay channel buffer
> *
> @@ -415,48 +448,33 @@ 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;
> + return NULL;
>
> spin_lock_init(&buf->rw_lock);
>
> + 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;
> + return buf;
>
> free_buf:
> relay_destroy_buf(buf);
> - buf = NULL;
> -free_name:
> - kfree(tmpname);
> -end:
> - return buf;
> + return NULL;
> }
>
> /**
> @@ -539,8 +557,8 @@ 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
> @@ -562,8 +580,6 @@ 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;
> @@ -578,7 +594,10 @@ 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);
>
> @@ -607,6 +626,62 @@ 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;
> + int err;
> + struct rchan_buf *buf;
> +
> + if (!chan || !base_filename)
> + return 1;
> +
> + strlcpy(chan->base_filename, base_filename, NAME_MAX);
> +
> + mutex_lock(&relay_channels_mutex);
> + if (unlikely(chan->has_base_filename))
> + goto out;
> + chan->has_base_filename = 1;
> + chan->parent = parent;
> + /*
> + * 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.
The following scenario will hide data :
cpu0 online
cpu1 online
tracing some stuff
cpu1 offline
relay_late_setup_files() is called.
You should iterate on all possible cpus and detect which ones have
buffers allocated.
> + */
> + for_each_online_cpu(i) {
> + buf = chan->buf[i];
> +
> + if (unlikely(!buf)) {
> + printk(KERN_ERR "relay_late_setup_files: "
> + "all CPUs should have buffers!\n");
> + goto out;
> + }
> +
> + err = relay_setup_buf_file(chan, buf, i);
> + if (unlikely(err))
> + goto out;
> + }
> + mutex_unlock(&relay_channels_mutex);
> +
> + return 0;
> +
> +out:
> + mutex_unlock(&relay_channels_mutex);
> + return 1;
> +}
> +
> +/**
> * relay_switch_subbuf - switch to a new sub-buffer
> * @buf: channel buffer
> * @length: size of current event
> @@ -629,8 +704,13 @@ 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))
> /*
> @@ -1241,9 +1321,8 @@ EXPORT_SYMBOL_GPL(relay_file_operations);
>
> static __init int relay_init(void)
> {
> -
Whitespace removal does not belong in this patch.
> hotcpu_notifier(relay_hotcpu_callback, 0);
> return 0;
> }
>
> -module_init(relay_init);
> +early_initcall(relay_init);
See discussion about "how early" in the previous patch of this patchset.
> --
> 1.5.5.4
>
--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68