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Added detail about syscall args.

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Remzi Arpaci-Dusseau
2018-02-20 15:26:49 -06:00
parent ff3f811e81
commit 299236f6c8
1 changed files with 10 additions and 1 deletions
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11
scheduling-xv6-lottery/README.md
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@@ -31,7 +31,8 @@ The second is `int getpinfo(struct pstat *)`. This routine returns some
information about all running processes, including how many times each has information about all running processes, including how many times each has
been chosen to run and the process ID of each. You can use this system call to been chosen to run and the process ID of each. You can use this system call to
build a variant of the command line program `ps`, which can then be called to build a variant of the command line program `ps`, which can then be called to
see what is going on. The structure `pstat` is defined below. see what is going on. The structure `pstat` is defined below; note, you cannot
change this structure, and must use it exactly as is.
Most of the code for the scheduler is quite localized and can be found in Most of the code for the scheduler is quite localized and can be found in
`proc.c`; the associated header file, `proc.h` is also quite useful to `proc.c`; the associated header file, `proc.h` is also quite useful to
@@ -62,6 +63,14 @@ struct pstat {
#endif // _PSTAT_H_ #endif // _PSTAT_H_
``` ```
Good examples of how to pass arguments into the kernel are found in existing
system calls. In particular, follow the path of `read()`, which will lead you
to `sys_read()`, which will show you how to use `argptr()` (and related calls)
to obtain a pointer that has been passed into the kernel. Note how careful the
kernel is with pointers passed from user space -- they are a security
threat(!), and thus must be checked very carefully before usage.
## Graph ## Graph
Beyond the usual code, you'll have to make a graph for this assignment. The Beyond the usual code, you'll have to make a graph for this assignment. The