[1.] Fault in init/do_mounts.c/change_floppy{} causes ramdisk file system
reads from floppy disks to fail
[2.] Full description of the problem/report:
I an trying to build a standalone Linux system using the process described
in the Bootdisk-HOWTO. HOWEVER I am using an *uncompressed* root file
system since I was unable to configure a compressed one that is small
enough to fit on a single floppy. I built:
- a boot floppy containing a bzImage Linux kernel and minimal
infrastructure that gets me to the point of being able to load a file
system from floppy onto ramdisk. This is the same kernel that I
use on my desktop every day.
- an ext2 root file system (4000 blocks) that holds a minimal set of
files/programs
- a set of 3 floppy disks that contains an uncompressed copy of the
ext2 root file system
When I try to boot the standalone system the following sequence of
events occurs:
- I load the boot floppy, and the kernel appears to load and
initialize correctly.
- The kernel prompts me to insert a floppy so it can load a file
system onto ramdisk.
- The code in init correctly determines that my floppy disk
contains an uncompressed ext2 file system.
- in init/do_mounts.c rd_load_image is called with argument "/dev/root"
- the for loop in this function starts reading from the first
floppy disk. Cachunk, cachunk.
- When 1440 1k block have been read, the function change_floppy is
called to move to the next floppy disk.
- change_floppy does something BROKEN. See below.
- The for loop in rd_load_image continues to try and read in more
uncompressed file system from the floppy, BUT THE READ DOES NOT
ACCESS the floppy drive. The reads in the for loop appear to
succeed, but nothing is actually transfered from the floppy
disk to the ramdisk.
- The same read failure happens for the third floppy disk.
- The end result is that I have a partial root file system on
ramdisk so nothing works after that.
The problem appears to be caused by this code
in init/do_mount.c/change_floppy{}
fd = open("/dev/root", O_RDWR | O_NDELAY, 0);
if (fd >= 0) {
sys_ioctl(fd, FDEJECT, 0);
close(fd);
}
When I comment this code out, init reads through the sequence of floppy
disks and correctly loads the uncompressed file system into a ramdisk.
[3.] Keywords: init do_mounts.c ramdisk "uncompressed ext2 file system"
[4.] Kernel version (from /proc/version):
Linux version 2.4.20 (root@pdp1) (gcc version 2.95.2 19991024 (release))
#14 Fri May 16 10:53:23 EDT 2003
[5.] Output of Oops: Not applicable
[6.] The problem can be reproduced by using dd to copy part of an existing root
ext2 file system onto 2 floppies as follows:
dd if=<ROOT_DEV> of=/dev/fd0 bs=1k count=1440
<CHANGE FLOPPY>
dd if=<ROOT_DEV> of=/dev/fd0 bs=1k count=1440 skip=1440
(it doesn't matter that you haven't copied the whole file system,
the read in init will fail on the second floppy).
Then build a boot kernel on a floppy with append parameters
load_ramdisk=1 prompt_ramdisk=1
Boot from the floppy, the kernel will prompt for the first file system
disk and correctly read it into a ramdisk. It will prompt
for the second floppy disk but the reads will fail, i.e. the
kernel will never read from the floppy drive.
[7.] Environment
[7.1.] Software (add the output of the ver_linux script here)
(This is from my running system which uses the same kernel as
the boot floppy that failed)
Linux pdp1 2.4.20 #14 Fri May 16 10:53:23 EDT 2003 i686 unknown
Gnu C 2.95.2
Gnu make 3.79.1
binutils 2.10.0.33
util-linux 2.10q
mount 2.10q
modutils 2.4.1
e2fsprogs 1.27
pcmcia-cs 3.1.22
Linux C Library x 1 root root 1382179 Jan 19 2001 /lib/libc.so.6
Dynamic linker (ldd) 2.2
Procps 2.0.7
Net-tools 1.57
Kbd 1.02
Sh-utils 2.0
Modules Loaded snd-seq-midi snd-seq-midi-event snd-seq snd-ens1370 snd-pcm snd-timer snd-rawmidi snd-seq-device snd-ak4531-codec snd soundcore
[7.2.] Processor information (from /proc/cpuinfo):
model name : AMD Athlon(TM) XP 2000+
[7.3.] Module information (from /proc/modules):
The system that fails never gets as far as loading modules.
[7.4.] Loaded driver and hardware information (/proc/ioports, /proc/iomem)
The system that fails never gets this far
[7.5.] PCI information ('lspci -vvv' as root)
Not relevant to this problem
[7.6.] SCSI information (from /proc/scsi/scsi)
Not relevant to this problem
[7.7.] Other information that might be relevant to the problem
The lilo configuration file on my boot floppy looks like this:
boot =/dev/fd0
install =/boot/boot.b
map =/boot/map
read-write
backup =/dev/null
compact
image =/boot/vmlinuz
append ="prompt_ramdisk=1 load_ramdisk=1"
label =Standalone
root =/dev/fd0
The kernel thinks my floppy disk is:
<6>Floppy drive(s): fd0 is 1.44M
<6>FDC 0 is a post-1991 82077
> I an trying to build a standalone Linux system using the process described
> in the Bootdisk-HOWTO. HOWEVER I am using an *uncompressed* root file
> system since I was unable to configure a compressed one that is small
> enough to fit on a single floppy. I built:
> - a boot floppy containing a bzImage Linux kernel and minimal
> infrastructure that gets me to the point of being able to load a file
> system from floppy onto ramdisk. This is the same kernel that I
> use on my desktop every day.
> - an ext2 root file system (4000 blocks) that holds a minimal set of
> files/programs
> - a set of 3 floppy disks that contains an uncompressed copy of the
> ext2 root file system
>
> When I try to boot the standalone system the following sequence of
> events occurs:
> - I load the boot floppy, and the kernel appears to load and
> initialize correctly.
> - The kernel prompts me to insert a floppy so it can load a file
> system onto ramdisk.
> - The code in init correctly determines that my floppy disk
> contains an uncompressed ext2 file system.
> - in init/do_mounts.c rd_load_image is called with argument "/dev/root"
> - the for loop in this function starts reading from the first
> floppy disk. Cachunk, cachunk.
> - When 1440 1k block have been read, the function change_floppy is
> called to move to the next floppy disk.
> - change_floppy does something BROKEN. See below.
> - The for loop in rd_load_image continues to try and read in more
> uncompressed file system from the floppy, BUT THE READ DOES NOT
> ACCESS the floppy drive. The reads in the for loop appear to
> succeed, but nothing is actually transfered from the floppy
> disk to the ramdisk.
> - The same read failure happens for the third floppy disk.
I saw similar behavior last time I tried to make an uncompressed root
fs that spanned five disks, (around 2.4.21-rc1), but I seem to
remember that it read disk 1, ignored disk 2, read disk 3, etc -
I.E. odd numbered disks were actually accessed.
I worked around the problem by making a _really_ minimal root fs that
fitted on a single disk, booting with that, then extracting everything
else I needed from a tar archive on another disk :-).
John.