PATCH: seq_file interface to provide large data chunks

Vladimir Kondratiev (
Thu, 10 Jul 2003 11:19:07 +0300

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
<>) 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;

/* 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;
m->index = pos;
+ goto Again;
if (!copied)
copied = err;

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