lkml.org 
[lkml]   [2005]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Date
Subject[-mm patch] relayfs: upgraded read() implementation
Hi,

The current relayfs read implementation works fine, but was designed
to be used mainly for 'draining' the buffer after a tracing run. It
turns out that people really want to be able to read from the buffer
during a live trace, for example the blktrace application submitted
recently:

http://marc.theaimsgroup.com/?l=linux-kernel&m=112480046405961&w=2

Here's an improved read implementation for relayfs which allows for
that.

This version has been tested pretty thoroughly, using both the
blktrace application and a new example I added to the relay-apps
tarball called 'readtest' which is basically a unit test for the read
functionality. All the tests I've come up with have passed and it
looks pretty solid at this point. Here's a link to the test code:

http://prdownloads.sourceforge.net/relayfs/relay-apps-0.8.tar.gz?download

Andrew, please apply.

Thanks,

Tom


Signed-off-by: Tom Zanussi <zanussi@us.ibm.com>

diff -urpN -X dontdiff linux-2.6.13-rc6-mm2/Documentation/filesystems/relayfs.txt linux-2.6.13-rc6-mm2-cur/Documentation/filesystems/relayfs.txt
--- linux-2.6.13-rc6-mm2/Documentation/filesystems/relayfs.txt 2005-08-25 19:28:59.000000000 -0500
+++ linux-2.6.13-rc6-mm2-cur/Documentation/filesystems/relayfs.txt 2005-08-25 17:07:48.000000000 -0500
@@ -82,10 +82,15 @@ mmap() results in channel buffer being
memory space. Note that you can't do a partial mmap - you must
map the entire file, which is NRBUF * SUBBUFSIZE.

-read() read the contents of a channel buffer. If there are active
- channel writers, results may be unpredictable - users should
- make sure that all logging to the channel has ended before
- using read().
+read() read the contents of a channel buffer. The bytes read are
+ 'consumed' by the reader i.e. they won't be available again
+ to subsequent reads. If the channel is being used in
+ no-overwrite mode (the default), it can be read at any time
+ even if there's an active kernel writer. If the channel is
+ being used in overwrite mode and there are active channel
+ writers, results may be unpredictable - users should make
+ sure that all logging to the channel has ended before using
+ read() with overwrite mode.

poll() POLLIN/POLLRDNORM/POLLERR supported. User applications are
notified when sub-buffer boundaries are crossed.
@@ -256,8 +261,8 @@ consulted.

The default subbuf_start() implementation, used if the client doesn't
define any callbacks, or doesn't define the subbuf_start() callback,
-implements the simplest possible 'overwrite' mode i.e. it does nothing
-but return 1.
+implements the simplest possible 'no-overwrite' mode i.e. it does
+nothing but return 0.

Header information can be reserved at the beginning of each sub-buffer
by calling the subbuf_start_reserve() helper function from within the
diff -urpN -X dontdiff linux-2.6.13-rc6-mm2/fs/relayfs/inode.c linux-2.6.13-rc6-mm2-cur/fs/relayfs/inode.c
--- linux-2.6.13-rc6-mm2/fs/relayfs/inode.c 2005-08-25 19:29:02.000000000 -0500
+++ linux-2.6.13-rc6-mm2-cur/fs/relayfs/inode.c 2005-08-25 18:21:31.000000000 -0500
@@ -295,101 +295,143 @@ static int relayfs_release(struct inode
}

/**
- * relayfs_read_start - find the first available byte to read
- *
- * If the read_pos is in the middle of padding, return the
- * position of the first actually available byte, otherwise
- * return the original value.
+ * relayfs_read_consume - update the consumed count for the buffer
*/
-static inline size_t relayfs_read_start(size_t read_pos,
- size_t avail,
- size_t start_subbuf,
- struct rchan_buf *buf)
+static void relayfs_read_consume(struct rchan_buf *buf,
+ size_t read_pos,
+ size_t bytes_consumed)
{
- size_t read_subbuf, adj_read_subbuf;
- size_t padding, padding_start, padding_end;
size_t subbuf_size = buf->chan->subbuf_size;
size_t n_subbufs = buf->chan->n_subbufs;
+ size_t read_subbuf;

- read_subbuf = read_pos / subbuf_size;
- adj_read_subbuf = (read_subbuf + start_subbuf) % n_subbufs;
+ if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
+ relay_subbufs_consumed(buf->chan, buf->cpu, 1);
+ buf->bytes_consumed = 0;
+ }

- if ((read_subbuf + 1) * subbuf_size <= avail) {
- padding = buf->padding[adj_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;
+ buf->bytes_consumed += bytes_consumed;
+ 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;
+ }
+}
+
+/**
+ * relayfs_read_avail - boolean, are there unconsumed bytes available?
+ */
+static int relayfs_read_avail(struct rchan_buf *buf, size_t read_pos)
+{
+ size_t bytes_produced, bytes_consumed, write_offset;
+ size_t subbuf_size = buf->chan->subbuf_size;
+ size_t n_subbufs = buf->chan->n_subbufs;
+ size_t produced = buf->subbufs_produced % n_subbufs;
+ size_t consumed = buf->subbufs_consumed % n_subbufs;
+
+ write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+
+ if (consumed > produced) {
+ if ((produced > n_subbufs) &&
+ (produced + n_subbufs - consumed <= n_subbufs))
+ produced += n_subbufs;
+ } else if (consumed == produced) {
+ if (buf->offset > subbuf_size) {
+ produced += n_subbufs;
+ if (buf->subbufs_produced == buf->subbufs_consumed)
+ consumed += n_subbufs;
}
}

- return read_pos;
+ if (buf->offset > subbuf_size)
+ bytes_produced = (produced - 1) * subbuf_size + write_offset;
+ else
+ bytes_produced = produced * subbuf_size + write_offset;
+ bytes_consumed = consumed * subbuf_size + buf->bytes_consumed;
+
+ if (bytes_produced == bytes_consumed)
+ return 0;
+
+ relayfs_read_consume(buf, read_pos, 0);
+
+ return 1;
}

/**
- * relayfs_read_end - return the end of available bytes to read
- *
- * If the read_pos is in the middle of a full sub-buffer, return
- * the padding-adjusted end of that sub-buffer, otherwise return
- * the position after the last byte written to the buffer. At
- * most, 1 sub-buffer can be read at a time.
- *
+ * relayfs_read_subbuf_avail - return bytes available in sub-buffer
*/
-static inline size_t relayfs_read_end(size_t read_pos,
- size_t avail,
- size_t start_subbuf,
- struct rchan_buf *buf)
+static size_t relayfs_read_subbuf_avail(size_t read_pos,
+ struct rchan_buf *buf)
{
- size_t padding, read_endpos, buf_offset;
- size_t read_subbuf, adj_read_subbuf;
+ size_t padding, avail = 0;
+ size_t read_subbuf, read_offset, write_subbuf, write_offset;
size_t subbuf_size = buf->chan->subbuf_size;
- size_t n_subbufs = buf->chan->n_subbufs;

- buf_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+ write_subbuf = (buf->data - buf->start) / subbuf_size;
+ write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
read_subbuf = read_pos / subbuf_size;
- adj_read_subbuf = (read_subbuf + start_subbuf) % n_subbufs;
+ read_offset = read_pos % subbuf_size;
+ padding = buf->padding[read_subbuf];

- if ((read_subbuf + 1) * subbuf_size <= avail) {
- padding = buf->padding[adj_read_subbuf];
- read_endpos = (read_subbuf + 1) * subbuf_size - padding;
+ if (read_subbuf == write_subbuf) {
+ if (read_offset + padding < write_offset)
+ avail = write_offset - (read_offset + padding);
} else
- read_endpos = read_subbuf * subbuf_size + buf_offset;
+ avail = (subbuf_size - padding) - read_offset;

- return read_endpos;
+ return avail;
}

/**
- * relayfs_read_avail - return total available along with buffer start
- *
- * Because buffers are circular, the 'beginning' of the buffer
- * depends on where the buffer was last written. If the writer
- * has cycled around the buffer, the beginning is defined to be
- * the beginning of the sub-buffer following the last sub-buffer
- * written to, otherwise it's the beginning of sub-buffer 0.
+ * relayfs_read_start_pos - find the first available byte to read
*
+ * If the read_pos is in the middle of padding, return the
+ * position of the first actually available byte, otherwise
+ * return the original value.
*/
-static inline size_t relayfs_read_avail(struct rchan_buf *buf,
- size_t *start_subbuf)
+static size_t relayfs_read_start_pos(size_t read_pos,
+ struct rchan_buf *buf)
{
- size_t avail, complete_subbufs, cur_subbuf, buf_offset;
+ 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;
+
+ 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;
+ }

- buf_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+ return read_pos;
+}

- if (buf->subbufs_produced >= n_subbufs) {
- complete_subbufs = n_subbufs - 1;
- cur_subbuf = (buf->data - buf->start) / subbuf_size;
- *start_subbuf = (cur_subbuf + 1) % n_subbufs;
- } else {
- complete_subbufs = buf->subbufs_produced;
- *start_subbuf = 0;
- }
+/**
+ * relayfs_read_end_pos - return the new read position
+ */
+static size_t relayfs_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;

- avail = complete_subbufs * subbuf_size + buf_offset;
+ 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)
+ end_pos = 0;

- return avail;
+ return end_pos;
}

/**
@@ -401,13 +443,6 @@ static inline size_t relayfs_read_avail(
*
* Reads count bytes or the number of bytes available in the
* current sub-buffer being read, whichever is smaller.
- *
- * NOTE: The results of reading a relayfs file which is currently
- * being written to are undefined. This is because the buffer is
- * circular and an active writer in the kernel could be
- * overwriting the data currently being read. Therefore read()
- * is mainly useful for reading the contents of a buffer after
- * logging has completed.
*/
static ssize_t relayfs_read(struct file *filp,
char __user *buffer,
@@ -416,33 +451,30 @@ static ssize_t relayfs_read(struct file
{
struct inode *inode = filp->f_dentry->d_inode;
struct rchan_buf *buf = RELAYFS_I(inode)->buf;
- size_t read_start, read_end, avail, start_subbuf;
- size_t buf_size = buf->chan->subbuf_size * buf->chan->n_subbufs;
+ size_t read_start, avail;
+ ssize_t ret = 0;
void *from;

- avail = relayfs_read_avail(buf, &start_subbuf);
- if (*ppos >= avail)
- return 0;
-
- read_start = relayfs_read_start(*ppos, avail, start_subbuf, buf);
- if (read_start == 0 && *ppos)
- return 0;
-
- read_end = relayfs_read_end(read_start, avail, start_subbuf, buf);
- if (read_end == read_start)
- return 0;
-
- from = buf->start + start_subbuf * buf->chan->subbuf_size + read_start;
- if (from >= buf->start + buf_size)
- from -= buf_size;
-
- count = min(count, read_end - read_start);
- if (copy_to_user(buffer, from, count))
- return -EFAULT;
-
- *ppos = read_start + count;
-
- return count;
+ down(&inode->i_sem);
+ if(!relayfs_read_avail(buf, *ppos))
+ goto out;
+
+ read_start = relayfs_read_start_pos(*ppos, buf);
+ avail = relayfs_read_subbuf_avail(read_start, buf);
+ if (!avail)
+ goto out;
+
+ from = buf->start + read_start;
+ ret = count = min(count, avail);
+ if (copy_to_user(buffer, from, count)) {
+ ret = -EFAULT;
+ goto out;
+ }
+ relayfs_read_consume(buf, read_start, count);
+ *ppos = relayfs_read_end_pos(buf, read_start, count);
+out:
+ up(&inode->i_sem);
+ return ret;
}

/**
@@ -481,6 +513,7 @@ struct file_operations relayfs_file_oper
.poll = relayfs_poll,
.mmap = relayfs_mmap,
.read = relayfs_read,
+ .llseek = no_llseek,
.release = relayfs_release,
};

diff -urpN -X dontdiff linux-2.6.13-rc6-mm2/fs/relayfs/relay.c linux-2.6.13-rc6-mm2-cur/fs/relayfs/relay.c
--- linux-2.6.13-rc6-mm2/fs/relayfs/relay.c 2005-08-25 19:29:02.000000000 -0500
+++ linux-2.6.13-rc6-mm2-cur/fs/relayfs/relay.c 2005-08-25 21:12:29.000000000 -0500
@@ -58,6 +58,9 @@ static int subbuf_start_default_callback
void *prev_subbuf,
size_t prev_padding)
{
+ if (relay_buf_full(buf))
+ return 0;
+
return 1;
}

@@ -120,6 +123,7 @@ static inline void __relay_reset(struct

buf->subbufs_produced = 0;
buf->subbufs_consumed = 0;
+ buf->bytes_consumed = 0;
buf->finalized = 0;
buf->data = buf->start;
buf->offset = 0;
@@ -262,6 +266,7 @@ struct rchan *relay_open(const char *bas
for_each_online_cpu(i) {
sprintf(tmpname, "%s%d", base_filename, i);
chan->buf[i] = relay_open_buf(chan, tmpname, parent);
+ chan->buf[i]->cpu = i;
if (!chan->buf[i])
goto free_bufs;
}
@@ -328,7 +333,7 @@ size_t relay_switch_subbuf(struct rchan_
return length;

toobig:
- printk(KERN_WARNING "relayfs: event too large (%u)\n", length);
+ printk(KERN_WARNING "relayfs: event too large (%Zd)\n", length);
WARN_ON(1);
return 0;
}
diff -urpN -X dontdiff linux-2.6.13-rc6-mm2/include/linux/relayfs_fs.h linux-2.6.13-rc6-mm2-cur/include/linux/relayfs_fs.h
--- linux-2.6.13-rc6-mm2/include/linux/relayfs_fs.h 2005-08-25 19:29:03.000000000 -0500
+++ linux-2.6.13-rc6-mm2-cur/include/linux/relayfs_fs.h 2005-08-24 00:16:37.000000000 -0500
@@ -22,7 +22,7 @@
/*
* Tracks changes to rchan_buf struct
*/
-#define RELAYFS_CHANNEL_VERSION 4
+#define RELAYFS_CHANNEL_VERSION 5

/*
* Per-cpu relay channel buffer
@@ -44,6 +44,8 @@ struct rchan_buf
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 */
+ unsigned int cpu; /* this buf's cpu */
} ____cacheline_aligned;

/*

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-08-25 23:27    [W:0.073 / U:32.416 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site