cat reading problem

cat reading problem

[Mockern]

Hello,

I tried to cat < /dev/mytty/ttyS3, but cat shows nothing. I attached here strace
  
cat < /dev/mytty/ttyS3 and cat < hello. Hello is just a file. As you can see the 

result of strace cat is identical, but in tty case I can't see nothing. Why does cat write nothing at my console?

Thank you, 

------------------------------------------------------------------------------------

root@test:/home# strace cat  < hello
│c│c│c│c│c│c│c│c│c│c│c│c..
munmap(0x40017000, 5664)                = 0
getuid32()                              = 0
getgid32()                              = 0
setgid32(0)                             = 0
setuid32(0)                             = 0
read(0, "Hello World!", 8192)           = 12
write(1, "Hello World!", 12Hello World!)            = 12
read(0, "", 8192)                       = 0
io_submit(0, 0x40200164, 0 <unfinished ... exit status 0>
Process 1520 detached
root@test:/home# strace cat  < /dev/mytty/ttyS3
│c│c│c│c│c│c│c│c│c│c│c│c│c.
getuid32()                              = 0
getgid32()                              = 0
setgid32(0)                             = 0
setuid32(0)                             = 0
read(0, "\376\377\377f\377\330\0000", 8192) = 8
write(1, "\376\377\377f\377\330\0000", 8│║ f0) = 8
read(0, "", 8192)                       = 0
io_submit(0, 0x40200164, 0 <unfinished ... exit status 0>
Process 1522 detached
root@test:/home#

Re: cat reading problem

[Arjan van de Ven]

> result of strace cat is identical, but in tty case I can't see nothing. Why does cat write nothing at my console?
> 
> Thank you, 
> 
> ------------------------------------------------------------------------------------
> 
> root@test:/home# strace cat  < hello
> │c│c│c│c│c│c│c│c│c│c│c│c..
> munmap(0x40017000, 5664)                = 0
> getuid32()                              = 0
> getgid32()                              = 0
> setgid32(0)                             = 0
> setuid32(0)                             = 0
> read(0, "Hello World!", 8192)           = 12
> write(1, "Hello World!", 12Hello World!)            = 12

you read "Hello World!" and you write "Hello World!" to the console

> read(0, "\376\377\377f\377\330\0000", 8192) = 8
> write(1, "\376\377\377f\377\330\0000", 8│║ f0) = 8

and here you read garbage from the input, so you write garbage out,
which probably confuses the heck out of your terminal for not being
correct UTF-8