relay - Remove padding-related code from relay_read()/relay_splice_read() et al.

Remove padding-related code from relay_read()/relay_splice_read() et al.

Because we no longer write padding, we no longer have to read it or account for it anywhere else, greatly simplifying the related code.

Signed-off-by Tom Zanussi <[email protected]>

---
 kernel/relay.c |  149
++++++++------------------------------------------------
 1 files changed, 20 insertions(+), 129 deletions(-)

kernel/relay.c +0 -25

index d382528..b55466d 100644
@@ -965,72 +965,13 @@ static void relay_file_read_consume(struct
 rchan_buf *buf,
 				    size_t bytes_consumed)
 {
 	size_t subbuf_size = buf->chan->subbuf_size;
-	size_t n_subbufs = buf->chan->n_subbufs;
-	size_t read_subbuf;
-
-	if (buf->subbufs_produced == buf->subbufs_consumed &&
-	    buf->offset == buf->bytes_consumed)
-		return;
-
-	if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
-		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
-		buf->bytes_consumed = 0;
-	}
 
 	buf->bytes_consumed += bytes_consumed;
-	if (!read_pos)
-		read_subbuf = buf->subbufs_consumed % n_subbufs;
-	else
-		read_subbuf = read_pos / buf->chan->subbuf_size;
-	if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
-		if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
-		    (buf->offset == subbuf_size))
-			return;
-		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
-		buf->bytes_consumed = 0;
-	}
-}
 
-/*
- *	relay_file_read_avail - boolean, are there unconsumed bytes

available?
- */
-static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)

kernel/relay.c +8 -42

-{
-	size_t subbuf_size = buf->chan->subbuf_size;
-	size_t n_subbufs = buf->chan->n_subbufs;
-	size_t produced = buf->subbufs_produced;
-	size_t consumed = buf->subbufs_consumed;
-
-	relay_file_read_consume(buf, read_pos, 0);
-
-	consumed = buf->subbufs_consumed;
-
-	if (unlikely(buf->offset > subbuf_size)) {
-		if (produced == consumed)
-			return 0;
-		return 1;
-	}
-
-	if (unlikely(produced - consumed >= n_subbufs)) {
-		consumed = produced - n_subbufs + 1;
-		buf->subbufs_consumed = consumed;
+	if (buf->bytes_consumed == subbuf_size) {
+		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 		buf->bytes_consumed = 0;
 	}
-
-	produced = (produced % n_subbufs) * subbuf_size + buf->offset;
-	consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
-
-	if (consumed > produced)
-		produced += n_subbufs * subbuf_size;
-
-	if (consumed == produced) {
-		if (buf->offset == subbuf_size &&
-		    buf->subbufs_produced > buf->subbufs_consumed)
-			return 1;
-		return 0;
-	}
-
-	return 1;
 }
 
 /**

@@ -1041,21 +982,19 @@ static int relay_file_read_avail(struct rchan_buf
 *buf, size_t read_pos)
 static size_t relay_file_read_subbuf_avail(size_t read_pos,
 					   struct rchan_buf *buf)
 {
-	size_t padding, avail = 0;
+	size_t avail;
 	size_t read_subbuf, read_offset, write_subbuf, write_offset;
 	size_t subbuf_size = buf->chan->subbuf_size;
 
 	write_subbuf = (buf->data - buf->start) / subbuf_size;
-	write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+	write_offset = buf->offset;
 	read_subbuf = read_pos / subbuf_size;
 	read_offset = read_pos % subbuf_size;
-	padding = buf->padding[read_subbuf];
 
-	if (read_subbuf == write_subbuf) {
-		if (read_offset + padding < write_offset)
-			avail = write_offset - (read_offset + padding);
-	} else
-		avail = (subbuf_size - padding) - read_offset;
+	avail = subbuf_size - read_offset;
+
+	if (read_subbuf == write_subbuf && read_offset < write_offset)
+		avail = write_offset - read_offset;
 
 	return avail;

}

kernel/relay.c +3 -14

@@ -1065,28 +1004,17 @@ static size_t
 relay_file_read_subbuf_avail(size_t read_pos,
  *	@read_pos: file read position
  *	@buf: relay channel buffer
  *
- *	If the @read_pos is in the middle of padding, return the
- *	position of the first actually available byte, otherwise
- *	return the original value.
+ *	If the @read_pos is 0, return the position of the first
+ *	unconsumed byte, otherwise return the original value.
  */
 static size_t relay_file_read_start_pos(size_t read_pos,
 					struct rchan_buf *buf)
 {
-	size_t read_subbuf, padding, padding_start, padding_end;
 	size_t subbuf_size = buf->chan->subbuf_size;
-	size_t n_subbufs = buf->chan->n_subbufs;
-	size_t consumed = buf->subbufs_consumed % n_subbufs;
+	size_t consumed = buf->subbufs_consumed % buf->chan->n_subbufs;
 
 	if (!read_pos)
 		read_pos = consumed * subbuf_size + buf->bytes_consumed;
-	read_subbuf = read_pos / subbuf_size;
-	padding = buf->padding[read_subbuf];
-	padding_start = (read_subbuf + 1) * subbuf_size - padding;
-	padding_end = (read_subbuf + 1) * subbuf_size;
-	if (read_pos >= padding_start && read_pos < padding_end) {
-		read_subbuf = (read_subbuf + 1) % n_subbufs;
-		read_pos = read_subbuf * subbuf_size;
-	}
 
 	return read_pos;

}

kernel/relay.c +2 -10

@@ -1101,17 +1029,9 @@ static size_t relay_file_read_end_pos(struct
 rchan_buf *buf,
 				      size_t read_pos,
 				      size_t count)
 {
-	size_t read_subbuf, padding, end_pos;
-	size_t subbuf_size = buf->chan->subbuf_size;
-	size_t n_subbufs = buf->chan->n_subbufs;
+	size_t end_pos = read_pos + count;
 
-	read_subbuf = read_pos / subbuf_size;
-	padding = buf->padding[read_subbuf];
-	if (read_pos % subbuf_size + count + padding == subbuf_size)
-		end_pos = (read_subbuf + 1) * subbuf_size;
-	else
-		end_pos = read_pos + count;
-	if (end_pos >= subbuf_size * n_subbufs)
+	if (end_pos >= buf->chan->subbuf_size * buf->chan->n_subbufs)
 		end_pos = 0;
 

kernel/relay.c +0 -3

 	return end_pos;

@@ -1165,9 +1085,6 @@ static ssize_t relay_file_read_subbufs(struct file
 *filp, loff_t *ppos,
 
 	mutex_lock(&filp->f_path.dentry->d_inode->i_mutex);
 	do {
-		if (!relay_file_read_avail(buf, *ppos))
-			break;
-
 		read_start = relay_file_read_start_pos(*ppos, buf);
 		avail = relay_file_read_subbuf_avail(read_start, buf);

kernel/relay.c +6 -31

 		if (!avail)

@@ -1242,8 +1159,7 @@ static int subbuf_splice_actor(struct file *in,
 			       loff_t *ppos,
 			       struct pipe_inode_info *pipe,
 			       size_t len,
-			       unsigned int flags,
-			       int *nonpad_ret)
+			       unsigned int flags)
 {
 	unsigned int pidx, poff, total_len, subbuf_pages, nr_pages, ret;
 	struct rchan_buf *rbuf = in->private_data;

@@ -1251,9 +1167,6 @@ static int subbuf_splice_actor(struct file *in,
 	uint64_t pos = (uint64_t) *ppos;
 	uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
 	size_t read_start = (size_t) do_div(pos, alloc_size);
-	size_t read_subbuf = read_start / subbuf_size;
-	size_t padding = rbuf->padding[read_subbuf];
-	size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
 	struct page *pages[PIPE_BUFFERS];
 	struct partial_page partial[PIPE_BUFFERS];
 	struct splice_pipe_desc spd = {

@@ -1265,7 +1178,8 @@ static int subbuf_splice_actor(struct file *in,
 		.spd_release = relay_page_release,
 	};
 
-	if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
+	if (rbuf->subbufs_produced == rbuf->subbufs_consumed &&
+	    rbuf->offset == rbuf->bytes_consumed)
 		return 0;
 
 	/*

@@ -1280,46 +1194,25 @@ static int subbuf_splice_actor(struct file *in,
 	nr_pages = min_t(unsigned int, subbuf_pages, PIPE_BUFFERS);
 
 	for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
-		unsigned int this_len, this_end, private;
-		unsigned int cur_pos = read_start + total_len;
+		unsigned int this_len;
 
 		if (!len)
 			break;
 
 		this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
-		private = this_len;
 
 		spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
 		spd.partial[spd.nr_pages].offset = poff;
 
-		this_end = cur_pos + this_len;
-		if (this_end >= nonpad_end) {
-			this_len = nonpad_end - cur_pos;
-			private = this_len + padding;
-		}
 		spd.partial[spd.nr_pages].len = this_len;
-		spd.partial[spd.nr_pages].private = private;
 
 		len -= this_len;
 		total_len += this_len;
 		poff = 0;
 		pidx = (pidx + 1) % subbuf_pages;
-
-		if (this_end >= nonpad_end) {
-			spd.nr_pages++;
-			break;
-		}
 	}
 
-	if (!spd.nr_pages)
-		return 0;
-
-	ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
-	if (ret < 0 || ret < total_len)
-		return ret;
-
-        if (read_start + ret == nonpad_end)
-                ret += padding;
+	ret = splice_to_pipe(pipe, &spd);
 
         return ret;
 }

@@ -1332,13 +1225,12 @@ static ssize_t relay_file_splice_read(struct
 file *in,
 {
 	ssize_t spliced;
 	int ret;
-	int nonpad_ret = 0;
 
 	ret = 0;
 	spliced = 0;
 
 	while (len && !spliced) {
-		ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
+		ret = subbuf_splice_actor(in, ppos, pipe, len, flags);
 		if (ret < 0)
 			break;

kernel/relay.c +1 -2

 		else if (!ret) {

@@ -1355,8 +1247,7 @@ static ssize_t relay_file_splice_read(struct file
 *in,
 			len = 0;
 		else
 			len -= ret;
-		spliced += nonpad_ret;
-		nonpad_ret = 0;
+		spliced += ret;
 	}
 

if (spliced)

Signature · 1 line

1.5.3.5

Quoted 7 lines · * Tom Zanussi ([email protected]) wrote:

Remove padding-related code from relay_read()/relay_splice_read() et al.

Because we no longer write padding, we no longer have to read it or account for it anywhere else, greatly simplifying the related code.

Signed-off-by Tom Zanussi <[email protected]>

Hi Tom,

This question might sound a bit dumb, but I'll ask anyway : why do you implement a splice_read rather than a splice_write in relay ?

splice_read allows reading information from a file or from a socket to a pipe, while splice_write does the opposite.

So if you implement a relay splice_read, you probably consider the relay buffers to be a "file", so you really have to send the information to a pipe, and then you have to use this pipe to send the data elsewhere.

My first reaction when looking at the splice implementation is that what we would really want is a splice_write which would take the data from a pipe (actually, we would have to write an actor which would make the relay buffer behave like a pipe) and write it either to disk or to a socket.

Is there something I am misunderstanding here ?

Thanks,

Mathieu

Quoted 292 lines

---
 kernel/relay.c |  149
++++++++------------------------------------------------
 1 files changed, 20 insertions(+), 129 deletions(-)

kernel/relay.c +0 -25

index d382528..b55466d 100644
@@ -965,72 +965,13 @@ static void relay_file_read_consume(struct
 rchan_buf *buf,
 				    size_t bytes_consumed)
 {
 	size_t subbuf_size = buf->chan->subbuf_size;
-	size_t n_subbufs = buf->chan->n_subbufs;
-	size_t read_subbuf;
-
-	if (buf->subbufs_produced == buf->subbufs_consumed &&
-	    buf->offset == buf->bytes_consumed)
-		return;
-
-	if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
-		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
-		buf->bytes_consumed = 0;
-	}
 
 	buf->bytes_consumed += bytes_consumed;
-	if (!read_pos)
-		read_subbuf = buf->subbufs_consumed % n_subbufs;
-	else
-		read_subbuf = read_pos / buf->chan->subbuf_size;
-	if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
-		if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
-		    (buf->offset == subbuf_size))
-			return;
-		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
-		buf->bytes_consumed = 0;
-	}
-}
 
-/*
- *	relay_file_read_avail - boolean, are there unconsumed bytes

available?
- */
-static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)

kernel/relay.c +8 -42

-{
-	size_t subbuf_size = buf->chan->subbuf_size;
-	size_t n_subbufs = buf->chan->n_subbufs;
-	size_t produced = buf->subbufs_produced;
-	size_t consumed = buf->subbufs_consumed;
-
-	relay_file_read_consume(buf, read_pos, 0);
-
-	consumed = buf->subbufs_consumed;
-
-	if (unlikely(buf->offset > subbuf_size)) {
-		if (produced == consumed)
-			return 0;
-		return 1;
-	}
-
-	if (unlikely(produced - consumed >= n_subbufs)) {
-		consumed = produced - n_subbufs + 1;
-		buf->subbufs_consumed = consumed;
+	if (buf->bytes_consumed == subbuf_size) {
+		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 		buf->bytes_consumed = 0;
 	}
-
-	produced = (produced % n_subbufs) * subbuf_size + buf->offset;
-	consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
-
-	if (consumed > produced)
-		produced += n_subbufs * subbuf_size;
-
-	if (consumed == produced) {
-		if (buf->offset == subbuf_size &&
-		    buf->subbufs_produced > buf->subbufs_consumed)
-			return 1;
-		return 0;
-	}
-
-	return 1;
 }
 
 /**

@@ -1041,21 +982,19 @@ static int relay_file_read_avail(struct rchan_buf
 *buf, size_t read_pos)
 static size_t relay_file_read_subbuf_avail(size_t read_pos,
 					   struct rchan_buf *buf)
 {
-	size_t padding, avail = 0;
+	size_t avail;
 	size_t read_subbuf, read_offset, write_subbuf, write_offset;
 	size_t subbuf_size = buf->chan->subbuf_size;
 
 	write_subbuf = (buf->data - buf->start) / subbuf_size;
-	write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+	write_offset = buf->offset;
 	read_subbuf = read_pos / subbuf_size;
 	read_offset = read_pos % subbuf_size;
-	padding = buf->padding[read_subbuf];
 
-	if (read_subbuf == write_subbuf) {
-		if (read_offset + padding < write_offset)
-			avail = write_offset - (read_offset + padding);
-	} else
-		avail = (subbuf_size - padding) - read_offset;
+	avail = subbuf_size - read_offset;
+
+	if (read_subbuf == write_subbuf && read_offset < write_offset)
+		avail = write_offset - read_offset;
 
 	return avail;

}

kernel/relay.c +3 -14

@@ -1065,28 +1004,17 @@ static size_t
 relay_file_read_subbuf_avail(size_t read_pos,
  *	@read_pos: file read position
  *	@buf: relay channel buffer
  *
- *	If the @read_pos is in the middle of padding, return the
- *	position of the first actually available byte, otherwise
- *	return the original value.
+ *	If the @read_pos is 0, return the position of the first
+ *	unconsumed byte, otherwise return the original value.
  */
 static size_t relay_file_read_start_pos(size_t read_pos,
 					struct rchan_buf *buf)
 {
-	size_t read_subbuf, padding, padding_start, padding_end;
 	size_t subbuf_size = buf->chan->subbuf_size;
-	size_t n_subbufs = buf->chan->n_subbufs;
-	size_t consumed = buf->subbufs_consumed % n_subbufs;
+	size_t consumed = buf->subbufs_consumed % buf->chan->n_subbufs;
 
 	if (!read_pos)
 		read_pos = consumed * subbuf_size + buf->bytes_consumed;
-	read_subbuf = read_pos / subbuf_size;
-	padding = buf->padding[read_subbuf];
-	padding_start = (read_subbuf + 1) * subbuf_size - padding;
-	padding_end = (read_subbuf + 1) * subbuf_size;
-	if (read_pos >= padding_start && read_pos < padding_end) {
-		read_subbuf = (read_subbuf + 1) % n_subbufs;
-		read_pos = read_subbuf * subbuf_size;
-	}
 
 	return read_pos;

}

kernel/relay.c +2 -10

@@ -1101,17 +1029,9 @@ static size_t relay_file_read_end_pos(struct
 rchan_buf *buf,
 				      size_t read_pos,
 				      size_t count)
 {
-	size_t read_subbuf, padding, end_pos;
-	size_t subbuf_size = buf->chan->subbuf_size;
-	size_t n_subbufs = buf->chan->n_subbufs;
+	size_t end_pos = read_pos + count;
 
-	read_subbuf = read_pos / subbuf_size;
-	padding = buf->padding[read_subbuf];
-	if (read_pos % subbuf_size + count + padding == subbuf_size)
-		end_pos = (read_subbuf + 1) * subbuf_size;
-	else
-		end_pos = read_pos + count;
-	if (end_pos >= subbuf_size * n_subbufs)
+	if (end_pos >= buf->chan->subbuf_size * buf->chan->n_subbufs)
 		end_pos = 0;
 

kernel/relay.c +0 -3

 	return end_pos;

@@ -1165,9 +1085,6 @@ static ssize_t relay_file_read_subbufs(struct file
 *filp, loff_t *ppos,
 
 	mutex_lock(&filp->f_path.dentry->d_inode->i_mutex);
 	do {
-		if (!relay_file_read_avail(buf, *ppos))
-			break;
-
 		read_start = relay_file_read_start_pos(*ppos, buf);
 		avail = relay_file_read_subbuf_avail(read_start, buf);

kernel/relay.c +6 -31

 		if (!avail)

@@ -1242,8 +1159,7 @@ static int subbuf_splice_actor(struct file *in,
 			       loff_t *ppos,
 			       struct pipe_inode_info *pipe,
 			       size_t len,
-			       unsigned int flags,
-			       int *nonpad_ret)
+			       unsigned int flags)
 {
 	unsigned int pidx, poff, total_len, subbuf_pages, nr_pages, ret;
 	struct rchan_buf *rbuf = in->private_data;

@@ -1251,9 +1167,6 @@ static int subbuf_splice_actor(struct file *in,
 	uint64_t pos = (uint64_t) *ppos;
 	uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
 	size_t read_start = (size_t) do_div(pos, alloc_size);
-	size_t read_subbuf = read_start / subbuf_size;
-	size_t padding = rbuf->padding[read_subbuf];
-	size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
 	struct page *pages[PIPE_BUFFERS];
 	struct partial_page partial[PIPE_BUFFERS];
 	struct splice_pipe_desc spd = {

@@ -1265,7 +1178,8 @@ static int subbuf_splice_actor(struct file *in,
 		.spd_release = relay_page_release,
 	};
 
-	if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
+	if (rbuf->subbufs_produced == rbuf->subbufs_consumed &&
+	    rbuf->offset == rbuf->bytes_consumed)
 		return 0;
 
 	/*

@@ -1280,46 +1194,25 @@ static int subbuf_splice_actor(struct file *in,
 	nr_pages = min_t(unsigned int, subbuf_pages, PIPE_BUFFERS);
 
 	for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
-		unsigned int this_len, this_end, private;
-		unsigned int cur_pos = read_start + total_len;
+		unsigned int this_len;
 
 		if (!len)
 			break;
 
 		this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
-		private = this_len;
 
 		spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
 		spd.partial[spd.nr_pages].offset = poff;
 
-		this_end = cur_pos + this_len;
-		if (this_end >= nonpad_end) {
-			this_len = nonpad_end - cur_pos;
-			private = this_len + padding;
-		}
 		spd.partial[spd.nr_pages].len = this_len;
-		spd.partial[spd.nr_pages].private = private;
 
 		len -= this_len;
 		total_len += this_len;
 		poff = 0;
 		pidx = (pidx + 1) % subbuf_pages;
-
-		if (this_end >= nonpad_end) {
-			spd.nr_pages++;
-			break;
-		}
 	}
 
-	if (!spd.nr_pages)
-		return 0;
-
-	ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
-	if (ret < 0 || ret < total_len)
-		return ret;
-
-        if (read_start + ret == nonpad_end)
-                ret += padding;
+	ret = splice_to_pipe(pipe, &spd);
 
         return ret;
 }

@@ -1332,13 +1225,12 @@ static ssize_t relay_file_splice_read(struct
 file *in,
 {
 	ssize_t spliced;
 	int ret;
-	int nonpad_ret = 0;
 
 	ret = 0;
 	spliced = 0;
 
 	while (len && !spliced) {
-		ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
+		ret = subbuf_splice_actor(in, ppos, pipe, len, flags);
 		if (ret < 0)
 			break;

kernel/relay.c +1 -2

 		else if (!ret) {

@@ -1355,8 +1247,7 @@ static ssize_t relay_file_splice_read(struct file
 *in,
 			len = 0;
 		else
 			len -= ret;
-		spliced += nonpad_ret;
-		nonpad_ret = 0;
+		spliced += ret;
 	}
 

if (spliced)

Signature · 1 line

1.5.3.5

The full relay patch.

Basically it includes the changes from the previous 11 that I posted and in addition completely separates the reading part of relay from the writing part. With the new changes, relay really does become just what its name says and and nothing more - it accepts pages from tracers, and relays the data to userspace via read(2) or splice(2) (and therefore sendfile(2)). It doesn't allocate any buffer space and provides no write functions - those are expected to be supplied by some other component such as the unified ring-buffer or any other tracer that might want relay pages of trace data to userspace.

Includes original relay write functions and buffers (the no-vmap page-based versions of the previous patchset), which have been split out into a new file called relay_pagewriter.c and provide one means of writing into pages and feeding them into relay. blktrace and kvmtrace have been 'ported' over to using pagewriter instead of relay directly.

Signed-off-by Tom Zanussi <[email protected]>

block/blktrace.c +0 -0

index eb9651c..8ba7094 100644

Quoted 28 lines · Tom Zanussi

The full relay patch.

Basically it includes the changes from the previous 11 that I posted and in addition completely separates the reading part of relay from the writing part. With the new changes, relay really does become just what its name says and and nothing more - it accepts pages from tracers, and relays the data to userspace via read(2) or splice(2) (and therefore sendfile(2)). It doesn't allocate any buffer space and provides no write functions - those are expected to be supplied by some other component such as the unified ring-buffer or any other tracer that might want relay pages of trace data to userspace.

Includes original relay write functions and buffers (the no-vmap page-based versions of the previous patchset), which have been split out into a new file called relay_pagewriter.c and provide one means of writing into pages and feeding them into relay. blktrace and kvmtrace have been 'ported' over to using pagewriter instead of relay directly.

Signed-off-by Tom Zanussi <[email protected]>

block/blktrace.c +0 -0

index eb9651c..8ba7094 100644
@@ -35,7 +35,7 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
 {
 	struct blk_io_trace *t;
 

block/blktrace.c static void trace_note(struct blk_trace *bt, pid_t pid, int action, · line 41

Quoted 5 lines

block/blktrace.c +1 -1

-	t = relay_reserve(bt->rchan, sizeof(*t) + len);
+	t = kmalloc(sizeof(*t) + len, GFP_KERNEL);
 	if (t) {
 		const int cpu = smp_processor_id();
 

Ugh, that's no good - it's both way too expensive, and also requires an atomic allocation.

Quoted 5 lines

block/blktrace.c +0 -0

@@ -166,7 +168,7 @@ void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	if (unlikely(tsk->btrace_seq != blktrace_seq))
 		trace_note_tsk(bt, tsk);
 

block/blktrace.c void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes, · line 174

Quoted 5 lines

block/blktrace.c +1 -1

-	t = relay_reserve(bt->rchan, sizeof(*t) + pdu_len);
+	t = kmalloc(sizeof(*t) + pdu_len, GFP_KERNEL);
 	if (t) {
 		cpu = smp_processor_id();
 		sequence = per_cpu_ptr(bt->sequence, cpu);

Ditto - I don't think this approach is viable at all, sorry!

Quoted 7 lines · * Tom Zanussi ([email protected]) wrote:

Remove padding-related code from relay_read()/relay_splice_read() et al.

Because we no longer write padding, we no longer have to read it or account for it anywhere else, greatly simplifying the related code.

Signed-off-by Tom Zanussi <[email protected]>

Hi Tom,

This question might sound a bit dumb, but I'll ask anyway : why do you implement a splice_read rather than a splice_write in relay ?

splice_read allows reading information from a file or from a socket to a pipe, while splice_write does the opposite.

So if you implement a relay splice_read, you probably consider the relay buffers to be a "file", so you really have to send the information to a pipe, and then you have to use this pipe to send the data elsewhere.

My first reaction when looking at the splice implementation is that what we would really want is a splice_write which would take the data from a pipe (actually, we would have to write an actor which would make the relay buffer behave like a pipe) and write it either to disk or to a socket.

Is there something I am misunderstanding here ?