Bug 952

Distribution:
Hardware Environment:
Software Environment:
Problem Description:

seq_file's (fs/seq_file.c) implementation for read() do not allow more than one
page to be returned for one system call. This differs from old read_proc_t one:
old implementation used to loop until there is more data to provide. 
This mean, programs that used to work fine with old implementation, will not
work with seq_file. I mean programs that do read(large_buffer) once. Strictly
say, correct action would be for program to loop while read()>0, but:
- 1. unfortunately, programs like 'xlogmaster' and 'mc' falls into this category;
- 2. by filling large buffer, we reduce number of syscalls
- 3. data returned by one syscall produced (or may be produced) atomically w.r.t
process context stuff, i.e. it is not the same to do one read() and multiple.

Steps to reproduce:

on 2.4.20 seq_file read() implementation is exactly the same, and good example
for large file that use seq_file is /proc/ksyms

do

strace -e read dd bs=10240 if=/proc/ksyms >/dev/null

It reveals that read() never return more than 4k.