On Tue, 2005-03-29 at 15:05 +0530, Gaurav Dhiman wrote:
> can you paste your strace results ?
> that might be of some help.
right, i forgot........here it is
NOTE: the "hello" getting printed in the length arg of
write is (I think!) the hello that cat wants to print!
[root@nellai root]# strace cat /dev/mydevice
execve("/bin/cat", ["cat", "/dev/mydevice"], [/* 35 vars */]) = 0
uname({sys="Linux", node="nellai", ...}) = 0
brk(0) = 0x804c3a4
open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or
directory)
open("/usr/lib/i686/mmx/libc.so.6", O_RDONLY) = -1 ENOENT (No such file
or directory)
stat64("/usr/lib/i686/mmx", 0xbfffed60) = -1 ENOENT (No such file or
directory)
open("/usr/lib/i686/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
stat64("/usr/lib/i686", 0xbfffed60) = -1 ENOENT (No such file or
directory)
open("/usr/lib/mmx/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
stat64("/usr/lib/mmx", 0xbfffed60) = -1 ENOENT (No such file or
directory)
open("/usr/lib/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
stat64("/usr/lib", {st_mode=S_IFDIR|0755, st_size=36864, ...}) = 0
open("/usr/openwin/lib/i686/mmx/libc.so.6", O_RDONLY) = -1 ENOENT (No
such file or directory)
stat64("/usr/openwin/lib/i686/mmx", 0xbfffed60) = -1 ENOENT (No such
file or directory)
open("/usr/openwin/lib/i686/libc.so.6", O_RDONLY) = -1 ENOENT (No such
file or directory)
stat64("/usr/openwin/lib/i686", 0xbfffed60) = -1 ENOENT (No such file or
directory)
open("/usr/openwin/lib/mmx/libc.so.6", O_RDONLY) = -1 ENOENT (No such
file or directory)
stat64("/usr/openwin/lib/mmx", 0xbfffed60) = -1 ENOENT (No such file or
directory)
open("/usr/openwin/lib/libc.so.6", O_RDONLY) = -1 ENOENT (No such file
or directory)
stat64("/usr/openwin/lib", 0xbfffed60) = -1 ENOENT (No such file or
directory)
open("/usr/X11R6/lib/i686/mmx/libc.so.6", O_RDONLY) = -1 ENOENT (No such
file or directory)
stat64("/usr/X11R6/lib/i686/mmx", 0xbfffed60) = -1 ENOENT (No such file
or directory)
open("/usr/X11R6/lib/i686/libc.so.6", O_RDONLY) = -1 ENOENT (No such
file or directory)
stat64("/usr/X11R6/lib/i686", 0xbfffed60) = -1 ENOENT (No such file or
directory)
open("/usr/X11R6/lib/mmx/libc.so.6", O_RDONLY) = -1 ENOENT (No such file
or directory)
stat64("/usr/X11R6/lib/mmx", 0xbfffed60) = -1 ENOENT (No such file or
directory)
open("/usr/X11R6/lib/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
stat64("/usr/X11R6/lib", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=66136, ...}) = 0
old_mmap(NULL, 66136, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40013000
close(3) = 0
open("/lib/i686/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\220Y\1"...,
1024) = 1024
fstat64(3, {st_mode=S_IFREG|0755, st_size=1395734, ...}) = 0
old_mmap(0x42000000, 1239844, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) =
0x42000000
mprotect(0x42126000, 35620, PROT_NONE) = 0
old_mmap(0x42126000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED,
3, 0x126000) = 0x42126000
old_mmap(0x4212b000, 15140, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|
MAP_ANONYMOUS, -1, 0) = 0x4212b000
close(3) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x40024000
munmap(0x40013000, 66136) = 0
brk(0) = 0x804c3a4
brk(0x804d3a4) = 0x804d3a4
brk(0x804e000) = 0x804e000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=1830272, ...}) = 0
mmap2(NULL, 1830272, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40025000
close(3) = 0
fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 3), ...}) = 0
open("/dev/mydevice", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFCHR|0644, st_rdev=makedev(254, 0), ...}) = 0
open("/dev/mydevice", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFCHR|0644, st_rdev=makedev(254, 0), ...}) = 0
read(3, "hello\0", 4096) = 6
write(1, "hello\0", 6hello) = 6
read(3, "", 4096) = 0
close(3) = 0
_exit(0) = ?
[root@nellai root]#
and here's the read method.......
const char msg[] = "hello";
static ssize_t Device_read(struct file *filp,char *buf,size_t
count,loff_t *offset)
{
if (*offset >= sizeof(msg) )
{
return 0;
}
count = sizeof(msg);
if(copy_to_user(buf, msg, count))
return -EFAULT;
*offset += count;
return count;
}
>
> Gaurav
>
>
> On Tue, 29 Mar 2005 14:42:18 +0530, Mandeep Sandhu
> <Mandeep_Sandhu@xxxxxxxxxxx> wrote:
> > hi all,
> >
> > I had written a small character driver under kernel 2.4.20.
> > For starters I had implemented it's read method only. This
> > would put a constant string "hello" into the user-space
> > buffer. The problem I'm seeing is that when i "cat" my device
> > it does not print anything on the console (i.e cat and not the
> > printk's in my driver...they get printed fine!). strace of cat
> > shows that it calls my drivers read method twice...first time
> > i copy the constant string into the user's buffer and return the
> > bytes copied....and on the second invocation i return 0 as there's
> > nothing more to read. strace shows cat writing out to the std.
> > output after the first read....but nothing comes on the console!!
> > if I put '\n' character in my constant string it prints out the
> > string correctly! I'm guessing the newline char causes the o/p
> > stream to be flushed....is this expected behavior??
> >
> > TIA,
> > -mandeep
> >
> > --
> > Kernelnewbies: Help each other learn about the Linux kernel.
> > Archive: http://mail.nl.linux.org/kernelnewbies/
> > FAQ: http://kernelnewbies.org/faq/
> >
> >
--
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Archive: http://mail.nl.linux.org/kernelnewbies/
FAQ: http://kernelnewbies.org/faq/
