vfs: seq_file: add helpers for data filling

Add two helpers that allow access to the seq_file's own buffer, but
hide the internal details of seq_files.

This allows easier implementation of special purpose filling
functions.  It also cleans up some existing functions which duplicated
the seq_file logic.

Make these inline functions in seq_file.h, as suggested by Al.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 38 insertions, 0 deletions

diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index 0c6a86b7959..8366d8f12e5 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -35,6 +35,44 @@ struct seq_operations {
 
 #define SEQ_SKIP 1
 
+/**
+ * seq_get_buf - get buffer to write arbitrary data to
+ * @m: the seq_file handle
+ * @bufp: the beginning of the buffer is stored here
+ *
+ * Return the number of bytes available in the buffer, or zero if
+ * there's no space.
+ */
+static inline size_t seq_get_buf(struct seq_file *m, char **bufp)
+{
+	BUG_ON(m->count > m->size);
+	if (m->count < m->size)
+		*bufp = m->buf + m->count;
+	else
+		*bufp = NULL;
+
+	return m->size - m->count;
+}
+
+/**
+ * seq_commit - commit data to the buffer
+ * @m: the seq_file handle
+ * @num: the number of bytes to commit
+ *
+ * Commit @num bytes of data written to a buffer previously acquired
+ * by seq_buf_get.  To signal an error condition, or that the data
+ * didn't fit in the available space, pass a negative @num value.
+ */
+static inline void seq_commit(struct seq_file *m, int num)
+{
+	if (num < 0) {
+		m->count = m->size;
+	} else {
+		BUG_ON(m->count + num > m->size);
+		m->count += num;
+	}
+}
+
 char *mangle_path(char *s, char *p, char *esc);
 int seq_open(struct file *, const struct seq_operations *);
 ssize_t seq_read(struct file *, char __user *, size_t, loff_t *);