[PATCH] relayfs: abolish prev_padding

Jason Xing
2025-05-07T13:42:58Z

From: Jason Xing <kernelxing@tencent.com>

prev_padding represents the unused space of certain subbuffer. If the
content of a call of relay_write() exceeds the limit of the remainder of
this subbuffer, it will skip storing in the rest space and record the
start point as buf->prev_padding in relay_switch_subbuf(). Since the buf
is a per-cpu big buffer, the point of prev_padding as a global value for
the whole buffer instead of a single subbuffer (whose padding info is
stored in buf->padding[]) seems meaningless from the real use cases, so
we don't bother to record it any more.

Reviewed-by: Yushan Zhou <katrinzhou@tencent.com>
Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
drivers/gpu/drm/i915/gt/uc/intel_guc_log.c | 3 +--
drivers/net/wwan/iosm/iosm_ipc_trace.c | 3 +--
drivers/net/wwan/t7xx/t7xx_port_trace.c | 2 +-
include/linux/relay.h | 5 +----
kernel/relay.c | 14 ++++++++------
kernel/trace/blktrace.c | 2 +-
6 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
index e8a04e476c57..09a64f224c49 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
@@ -220,8 +220,7 @@ static int guc_action_control_log(struct intel_guc *guc, bool enable,
*/
static int subbuf_start_callback(struct rchan_buf *buf,
void *subbuf,
- void *prev_subbuf,
- size_t prev_padding)
+ void *prev_subbuf)
{
/*
* Use no-overwrite mode by default, where relay will stop accepting
diff --git a/drivers/net/wwan/iosm/iosm_ipc_trace.c b/drivers/net/wwan/iosm/iosm_ipc_trace.c
index eeecfa3d10c5..9656254c1c6c 100644
--- a/drivers/net/wwan/iosm/iosm_ipc_trace.c
+++ b/drivers/net/wwan/iosm/iosm_ipc_trace.c
@@ -51,8 +51,7 @@ static int ipc_trace_remove_buf_file_handler(struct dentry *dentry)
}

static int ipc_trace_subbuf_start_handler(struct rchan_buf *buf, void *subbuf,
- void *prev_subbuf,
- size_t prev_padding)
+ void *prev_subbuf)
{
if (relay_buf_full(buf)) {
pr_err_ratelimited("Relay_buf full dropping traces");
diff --git a/drivers/net/wwan/t7xx/t7xx_port_trace.c b/drivers/net/wwan/t7xx/t7xx_port_trace.c
index 4ed8b4e29bf1..f16d3b01302c 100644
--- a/drivers/net/wwan/t7xx/t7xx_port_trace.c
+++ b/drivers/net/wwan/t7xx/t7xx_port_trace.c
@@ -33,7 +33,7 @@ static int t7xx_trace_remove_buf_file_handler(struct dentry *dentry)
}

static int t7xx_trace_subbuf_start_handler(struct rchan_buf *buf, void *subbuf,
- void *prev_subbuf, size_t prev_padding)
+ void *prev_subbuf)
{
if (relay_buf_full(buf)) {
pr_err_ratelimited("Relay_buf full dropping traces");
diff --git a/include/linux/relay.h b/include/linux/relay.h
index 72b876dd5cb8..f80b0eb1e905 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -47,7 +47,6 @@ struct rchan_buf
unsigned int page_count; /* number of current buffer pages */
unsigned int finalized; /* buffer has been finalized */
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 */
@@ -84,7 +83,6 @@ struct rchan_callbacks
* @buf: the channel buffer containing the new sub-buffer
* @subbuf: the start of the new sub-buffer
* @prev_subbuf: the start of the previous sub-buffer
- * @prev_padding: unused space at the end of previous sub-buffer
*
* The client should return 1 to continue logging, 0 to stop
* logging.
@@ -100,8 +98,7 @@ struct rchan_callbacks
*/
int (*subbuf_start) (struct rchan_buf *buf,
void *subbuf,
- void *prev_subbuf,
- size_t prev_padding);
+ void *prev_subbuf);

/*
* create_buf_file - create file to represent a relay channel buffer
diff --git a/kernel/relay.c b/kernel/relay.c
index 5ac7e711e4b6..5aeb9226e238 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -250,13 +250,13 @@ EXPORT_SYMBOL_GPL(relay_buf_full);
*/

static int relay_subbuf_start(struct rchan_buf *buf, void *subbuf,
- void *prev_subbuf, size_t prev_padding)
+ void *prev_subbuf)
{
if (!buf->chan->cb->subbuf_start)
return !relay_buf_full(buf);

return buf->chan->cb->subbuf_start(buf, subbuf,
- prev_subbuf, prev_padding);
+ prev_subbuf);
}

/**
@@ -302,7 +302,7 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init)
for (i = 0; i < buf->chan->n_subbufs; i++)
buf->padding[i] = 0;

- relay_subbuf_start(buf, buf->data, NULL, 0);
+ relay_subbuf_start(buf, buf->data, NULL);
}

/**
@@ -664,9 +664,11 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
goto toobig;

if (buf->offset != buf->chan->subbuf_size + 1) {
- buf->prev_padding = buf->chan->subbuf_size - buf->offset;
+ size_t prev_padding;
+
+ prev_padding = buf->chan->subbuf_size - buf->offset;
old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
- buf->padding[old_subbuf] = buf->prev_padding;
+ buf->padding[old_subbuf] = prev_padding;
buf->subbufs_produced++;
if (buf->dentry)
d_inode(buf->dentry)->i_size +=
@@ -691,7 +693,7 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
new = buf->start + new_subbuf * buf->chan->subbuf_size;
buf->offset = 0;
- if (!relay_subbuf_start(buf, new, old, buf->prev_padding)) {
+ if (!relay_subbuf_start(buf, new, old)) {
buf->offset = buf->chan->subbuf_size + 1;
return 0;
}
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 3679a6d18934..d1a89714e805 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -461,7 +461,7 @@ static const struct file_operations blk_msg_fops = {
* the user space app in telling how many lost events there were.
*/
static int blk_subbuf_start_callback(struct rchan_buf *buf, void *subbuf,
- void *prev_subbuf, size_t prev_padding)
+ void *prev_subbuf)
{
struct blk_trace *bt;

--
2.43.5