lab5-questionary.txt

=== This template file contains questions you need to answer.
=== Fill your answers on appropriate blank lines only.
=== Don't start any line with three equal signs "===".
=== Don't edit any lines starting from three equal signs.
=== Use C notation to write numbers: 42 for decimal, 0x2a for hexadecimal.
=== We may check most of the answers automatically, so "forty two" or
=== "26+16" won't work for this example. Spaces are mostly ignored, so
=== "  42  " is OK (without quotes of course). 
=== When asked to specify address & instruction, do it in the form of
=== gdb output "ADDRESS: INSTRUCTION", for example "0x7c26:  or  $0x1,%eax"
=== Don't make lines longer than 80 characters. You don't need to fit your
=== answer in a single line, you can start a new line at will.
=== However, when asked to fill "a table" make each table raw a single line.

=== Q How much disk space can be addressed by a single bitmap block
===   when size of a block is 4KB? (number in _bytes_)
134217728

=== Q How much disk space can be addressed by a single bitmap block
===   when size of a block is 512B? (number in _bytes_)
16777216

=== Q What is a maximum supported file size in JOS FS? (number in _bytes_)
4235264

=== Q Did you have to do anything else to ensure that the I/O
===   privilege setting is saved and restored properly when you
===   subsequently switch from one environment to another? Why? 
===   (free form)
No, the way we designed the kernel is that only, running with CPL == 0 
privilege We can change the EFLAGS registers, and when forking the EFLAGS
register goes from father to son, so unless the fs env forks its self 
(and its not ) then the file system env is the only env who can run with
that privilege.

=== Q How long approximately did it take you to do this lab?
===   (number of hours for all partners combined)
The lab itself - 14 hours (combined)
The challenge - 6 hours (combined)
====================================================================
=== Q What challenge(s) have you chosen to implement? (specify
===   challenge numbers separated by spaces, if more than one)
3

=== Q If the challenge requires changing the kernel source, list the
===   files which you have changed/added during implementation.
===   (one file per line, relative to lab directory containing .git/)
kern/syscall.c
inc/lib.h
lib/spawn.c
lib/syscall.c
inc/syscall.h
=== Q Describe you solution.
===   (free form, up to 500 words, don't need to use all 500!)

We have chosen to do the unix like exec challenge:

In our solution we had to come up with a way to save the binary data
And parameters given in argv our memory while cleaning the current 
environment and loading a new one onto it.

We had to load the binary from the file system and store it somewhere
While we manage the environment setup for it. We decided to use a temp
Memory region called EXEC_TEMP and UTEMP. The first used to store the
Loaded binary parts from the file descriptor and the second is used as
a temporary placement for our new stack, which is already holding the
arguments for the binary we’re going to execute.

In our solution we first loaded to binary to the temp region, and then
We called a similar version of spawn’s ‘init_stack’ to set the new stack
For the binary. After we set the information that the new env will need
We called the system call sys_exec.
Inside the system call we set the tf_eip to the binary entry point and
Copy and stack and binary back into the current mappings of the incoming
New env. After we set everything up and we call env_run so it will load
The new env from the chosen entry point using the same process to run 
The binary and a unix exec version would have done.