PATCH: seq_file interface to provide large data chunks

[Vladimir Kondratiev]

seq_file interface, as it exist in last official kernel, never provides 
more then one page for each 'read' call. Old read_proc_t did loop to 
fill more than one page.

Following patch against 2.4.21 fixes seq_file to provide more than one 
page if user requests it.
Many programs do read(large_buffer) once, instead of looping while 
read()>0. They work wrong with seq_file. Also, one may expect read() to 
provide whole information atomically (OK, relatively to other process 
context stuff).
This patch loops over while some space remains in user provided buffer.

I am not subscribed to lkml, thus please cc: me (Vladimir Kondratiev 
<[e-mail]>) explicitly.

--- linux-2.4.21/fs/seq_file.c    2003-06-13 17:51:37.000000000 +0300
+++ linux/fs/seq_file.c    2003-07-10 10:47:53.000000000 +0300
@@ -55,6 +55,7 @@
         return -EPIPE;
 
     down(&m->sem);
+Again:
     /* grab buffer if we didn't have one */
     if (!m->buf) {
         m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
@@ -123,11 +124,14 @@
         goto Efault;
     copied += n;
     m->count -= n;
+    size -= n;
+    buf += n;
     if (m->count)
         m->from = n;
     else
         pos++;
     m->index = pos;
+    goto Again;
 Done:
     if (!copied)
         copied = err;