At the kernel summit, there was some discussion of relayfs and the
consensus was that it didn't make sense for relayfs to not implement
read(). So here's a read implementation...
Andrew, please apply.
Tom
Signed-off-by: Tom Zanussi <[email protected]>
diff -urpN -X dontdiff linux-2.6.13-rc4-mm1/fs/relayfs/inode.c linux-2.6.13-rc4-mm1-cur/fs/relayfs/inode.c
--- linux-2.6.13-rc4-mm1/fs/relayfs/inode.c 2005-08-05 10:14:34.000000000 -0500
+++ linux-2.6.13-rc4-mm1-cur/fs/relayfs/inode.c 2005-08-05 10:17:47.000000000 -0500
@@ -232,7 +232,7 @@ int relayfs_remove_dir(struct dentry *de
*
* Increments the channel buffer refcount.
*/
-int relayfs_open(struct inode *inode, struct file *filp)
+static int relayfs_open(struct inode *inode, struct file *filp)
{
struct rchan_buf *buf = RELAYFS_I(inode)->buf;
kref_get(&buf->kref);
@@ -247,7 +247,7 @@ int relayfs_open(struct inode *inode, st
*
* Calls upon relay_mmap_buf to map the file into user space.
*/
-int relayfs_mmap(struct file *filp, struct vm_area_struct *vma)
+static int relayfs_mmap(struct file *filp, struct vm_area_struct *vma)
{
struct inode *inode = filp->f_dentry->d_inode;
return relay_mmap_buf(RELAYFS_I(inode)->buf, vma);
@@ -260,7 +260,7 @@ int relayfs_mmap(struct file *filp, stru
*
* Poll implemention.
*/
-unsigned int relayfs_poll(struct file *filp, poll_table *wait)
+static unsigned int relayfs_poll(struct file *filp, poll_table *wait)
{
unsigned int mask = 0;
struct inode *inode = filp->f_dentry->d_inode;
@@ -286,7 +286,7 @@ unsigned int relayfs_poll(struct file *f
* Decrements the channel refcount, as the filesystem is
* no longer using it.
*/
-int relayfs_release(struct inode *inode, struct file *filp)
+static int relayfs_release(struct inode *inode, struct file *filp)
{
struct rchan_buf *buf = RELAYFS_I(inode)->buf;
kref_put(&buf->kref, relay_remove_buf);
@@ -295,6 +295,157 @@ int relayfs_release(struct inode *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.
+ */
+static inline unsigned int relayfs_read_start(unsigned int read_pos,
+ unsigned int avail,
+ unsigned int start_subbuf,
+ struct rchan_buf *buf)
+{
+ unsigned int read_subbuf, adj_read_subbuf;
+ unsigned int padding, padding_start, padding_end;
+ unsigned int subbuf_size = buf->chan->subbuf_size;
+ unsigned int n_subbufs = buf->chan->n_subbufs;
+
+ read_subbuf = read_pos / subbuf_size;
+ adj_read_subbuf = (read_subbuf + start_subbuf) % n_subbufs;
+
+ 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;
+ }
+ }
+
+ return read_pos;
+}
+
+/**
+ * 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.
+ *
+ */
+static inline unsigned int relayfs_read_end(unsigned int read_pos,
+ unsigned int avail,
+ unsigned int start_subbuf,
+ struct rchan_buf *buf)
+{
+ unsigned int padding, read_endpos, buf_offset;
+ unsigned int read_subbuf, adj_read_subbuf;
+ unsigned int subbuf_size = buf->chan->subbuf_size;
+ unsigned int n_subbufs = buf->chan->n_subbufs;
+
+ buf_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+ read_subbuf = read_pos / subbuf_size;
+ adj_read_subbuf = (read_subbuf + start_subbuf) % n_subbufs;
+
+ if ((read_subbuf + 1) * subbuf_size <= avail) {
+ padding = buf->padding[adj_read_subbuf];
+ read_endpos = (read_subbuf + 1) * subbuf_size - padding;
+ } else
+ read_endpos = read_subbuf * subbuf_size + buf_offset;
+
+ return read_endpos;
+}
+
+/**
+ * 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.
+ *
+ */
+static inline unsigned int relayfs_read_avail(struct rchan_buf *buf,
+ unsigned int *start_subbuf)
+{
+ unsigned int avail, complete_subbufs, cur_subbuf, buf_offset;
+ unsigned int subbuf_size = buf->chan->subbuf_size;
+ unsigned int n_subbufs = buf->chan->n_subbufs;
+
+ buf_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+
+ 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;
+ }
+
+ avail = complete_subbufs * subbuf_size + buf_offset;
+
+ return avail;
+}
+
+/**
+ * relayfs_read - read file op for relayfs files
+ * @filp: the file
+ * @buffer: the userspace buffer
+ * @count: number of bytes to read
+ * @ppos: position to read from
+ *
+ * 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,
+ size_t count,
+ loff_t *ppos)
+{
+ struct inode *inode = filp->f_dentry->d_inode;
+ struct rchan_buf *buf = RELAYFS_I(inode)->buf;
+ unsigned int read_start, read_end, avail, start_subbuf;
+ unsigned int buf_size = buf->chan->subbuf_size * buf->chan->n_subbufs;
+ 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;
+}
+
+/**
* relayfs alloc_inode() implementation
*/
static struct inode *relayfs_alloc_inode(struct super_block *sb)
@@ -329,6 +480,7 @@ struct file_operations relayfs_file_oper
.open = relayfs_open,
.poll = relayfs_poll,
.mmap = relayfs_mmap,
+ .read = relayfs_read,
.release = relayfs_release,
};
@@ -404,10 +556,6 @@ static void __exit exit_relayfs_fs(void)
module_init(init_relayfs_fs)
module_exit(exit_relayfs_fs)
-EXPORT_SYMBOL_GPL(relayfs_open);
-EXPORT_SYMBOL_GPL(relayfs_poll);
-EXPORT_SYMBOL_GPL(relayfs_mmap);
-EXPORT_SYMBOL_GPL(relayfs_release);
EXPORT_SYMBOL_GPL(relayfs_file_operations);
EXPORT_SYMBOL_GPL(relayfs_create_dir);
EXPORT_SYMBOL_GPL(relayfs_remove_dir);
-
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