Commit 20d8b67c authored by Eduard - Gabriel Munteanu's avatar Eduard - Gabriel Munteanu Committed by Linus Torvalds

relay: add buffer-only channels; useful for early logging

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.

[kosaki.motohiro@jp.fujitsu.com: build fix]
Signed-off-by: default avatarEduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7babe8db
...@@ -294,6 +294,16 @@ user-defined data with a channel, and is immediately available ...@@ -294,6 +294,16 @@ user-defined data with a channel, and is immediately available
(including in create_buf_file()) via chan->private_data or (including in create_buf_file()) via chan->private_data or
buf->chan->private_data. 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' Channel 'modes'
--------------- ---------------
......
...@@ -48,6 +48,7 @@ struct rchan_buf ...@@ -48,6 +48,7 @@ struct rchan_buf
size_t *padding; /* padding counts per sub-buffer */ size_t *padding; /* padding counts per sub-buffer */
size_t prev_padding; /* temporary variable */ size_t prev_padding; /* temporary variable */
size_t bytes_consumed; /* bytes consumed in cur read subbuf */ 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 */ unsigned int cpu; /* this buf's cpu */
} ____cacheline_aligned; } ____cacheline_aligned;
...@@ -68,6 +69,7 @@ struct rchan ...@@ -68,6 +69,7 @@ struct rchan
int is_global; /* One global buffer ? */ int is_global; /* One global buffer ? */
struct list_head list; /* for channel list */ struct list_head list; /* for channel list */
struct dentry *parent; /* parent dentry passed to open */ struct dentry *parent; /* parent dentry passed to open */
int has_base_filename; /* has a filename associated? */
char base_filename[NAME_MAX]; /* saved base filename */ char base_filename[NAME_MAX]; /* saved base filename */
}; };
...@@ -169,6 +171,9 @@ struct rchan *relay_open(const char *base_filename, ...@@ -169,6 +171,9 @@ struct rchan *relay_open(const char *base_filename,
size_t n_subbufs, size_t n_subbufs,
struct rchan_callbacks *cb, struct rchan_callbacks *cb,
void *private_data); 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_close(struct rchan *chan);
extern void relay_flush(struct rchan *chan); extern void relay_flush(struct rchan *chan);
extern void relay_subbufs_consumed(struct rchan *chan, extern void relay_subbufs_consumed(struct rchan *chan,
......
...@@ -407,6 +407,35 @@ void relay_reset(struct rchan *chan) ...@@ -407,6 +407,35 @@ void relay_reset(struct rchan *chan)
} }
EXPORT_SYMBOL_GPL(relay_reset); EXPORT_SYMBOL_GPL(relay_reset);
static inline void relay_set_buf_dentry(struct rchan_buf *buf,
struct dentry *dentry)
{
buf->dentry = dentry;
buf->dentry->d_inode->i_size = buf->early_bytes;
}
static struct dentry *relay_create_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)
return NULL;
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);
return dentry;
}
/* /*
* relay_open_buf - create a new relay channel buffer * relay_open_buf - create a new relay channel buffer
* *
...@@ -416,45 +445,34 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu) ...@@ -416,45 +445,34 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
{ {
struct rchan_buf *buf = NULL; struct rchan_buf *buf = NULL;
struct dentry *dentry; struct dentry *dentry;
char *tmpname;
if (chan->is_global) if (chan->is_global)
return chan->buf[0]; 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); buf = relay_create_buf(chan);
if (!buf) if (!buf)
goto free_name; return NULL;
if (chan->has_base_filename) {
dentry = relay_create_buf_file(chan, buf, cpu);
if (!dentry)
goto free_buf;
relay_set_buf_dentry(buf, dentry);
}
buf->cpu = cpu; buf->cpu = cpu;
__relay_reset(buf, 1); __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) { if(chan->is_global) {
chan->buf[0] = buf; chan->buf[0] = buf;
buf->cpu = 0; buf->cpu = 0;
} }
goto free_name; return buf;
free_buf: free_buf:
relay_destroy_buf(buf); relay_destroy_buf(buf);
buf = NULL; return NULL;
free_name:
kfree(tmpname);
end:
return buf;
} }
/** /**
...@@ -537,8 +555,8 @@ static int __cpuinit relay_hotcpu_callback(struct notifier_block *nb, ...@@ -537,8 +555,8 @@ static int __cpuinit relay_hotcpu_callback(struct notifier_block *nb,
/** /**
* relay_open - create a new relay channel * relay_open - create a new relay channel
* @base_filename: base name of files to create * @base_filename: base name of files to create, %NULL for buffering only
* @parent: dentry of parent directory, %NULL for root directory * @parent: dentry of parent directory, %NULL for root directory or buffer
* @subbuf_size: size of sub-buffers * @subbuf_size: size of sub-buffers
* @n_subbufs: number of sub-buffers * @n_subbufs: number of sub-buffers
* @cb: client callback functions * @cb: client callback functions
...@@ -560,8 +578,6 @@ struct rchan *relay_open(const char *base_filename, ...@@ -560,8 +578,6 @@ struct rchan *relay_open(const char *base_filename,
{ {
unsigned int i; unsigned int i;
struct rchan *chan; struct rchan *chan;
if (!base_filename)
return NULL;
if (!(subbuf_size && n_subbufs)) if (!(subbuf_size && n_subbufs))
return NULL; return NULL;
...@@ -576,7 +592,10 @@ struct rchan *relay_open(const char *base_filename, ...@@ -576,7 +592,10 @@ struct rchan *relay_open(const char *base_filename,
chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs); chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
chan->parent = parent; chan->parent = parent;
chan->private_data = private_data; 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); setup_callbacks(chan, cb);
kref_init(&chan->kref); kref_init(&chan->kref);
...@@ -604,6 +623,94 @@ struct rchan *relay_open(const char *base_filename, ...@@ -604,6 +623,94 @@ struct rchan *relay_open(const char *base_filename,
} }
EXPORT_SYMBOL_GPL(relay_open); EXPORT_SYMBOL_GPL(relay_open);
struct rchan_percpu_buf_dispatcher {
struct rchan_buf *buf;
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.
* 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)
{
int err = 0;
unsigned int i, curr_cpu;
unsigned long flags;
struct dentry *dentry;
struct rchan_percpu_buf_dispatcher disp;
if (!chan || !base_filename)
return -EINVAL;
strlcpy(chan->base_filename, base_filename, NAME_MAX);
mutex_lock(&relay_channels_mutex);
/* Is chan already set up? */
if (unlikely(chan->has_base_filename))
return -EEXIST;
chan->has_base_filename = 1;
chan->parent = parent;
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) {
if (unlikely(!chan->buf[i])) {
printk(KERN_ERR "relay_late_setup_files: CPU %u "
"has no buffer, it must have!\n", i);
BUG();
err = -EINVAL;
break;
}
dentry = relay_create_buf_file(chan, chan->buf[i], i);
if (unlikely(!dentry)) {
err = -EINVAL;
break;
}
if (curr_cpu == i) {
local_irq_save(flags);
relay_set_buf_dentry(chan->buf[i], dentry);
local_irq_restore(flags);
} else {
disp.buf = chan->buf[i];
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;
}
/** /**
* relay_switch_subbuf - switch to a new sub-buffer * relay_switch_subbuf - switch to a new sub-buffer
* @buf: channel buffer * @buf: channel buffer
...@@ -627,8 +734,13 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length) ...@@ -627,8 +734,13 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs; old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
buf->padding[old_subbuf] = buf->prev_padding; buf->padding[old_subbuf] = buf->prev_padding;
buf->subbufs_produced++; buf->subbufs_produced++;
buf->dentry->d_inode->i_size += buf->chan->subbuf_size - if (buf->dentry)
buf->padding[old_subbuf]; 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(); smp_mb();
if (waitqueue_active(&buf->read_wait)) if (waitqueue_active(&buf->read_wait))
/* /*
...@@ -1237,4 +1349,4 @@ static __init int relay_init(void) ...@@ -1237,4 +1349,4 @@ static __init int relay_init(void)
return 0; return 0;
} }
module_init(relay_init); early_initcall(relay_init);
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