Clarify page fault handler for get/put_user().

[pintos-anon] / doc / userprog.texi

diff --git a/doc/userprog.texi b/doc/userprog.texi
index 880fe46f74ffc4e26139f59f9f4428391247eca3..d5eee6d0814675ef5195935dc61be786ae74c1b2 100644 (file)
--- a/doc/userprog.texi
+++ b/doc/userprog.texi
@@ -295,8 +295,8 @@ Kernel virtual memory is global.  It is always mapped the same way,
 regardless of what user process or kernel thread is running.  In
 Pintos, kernel virtual memory is mapped one-to-one to physical
 memory, starting at @code{PHYS_BASE}.  That is, virtual address
-@code{PHYS_ADDR} accesses physical
-address 0, virtual address @code{PHYS_ADDR} + @t{0x1234} access
+@code{PHYS_BASE} accesses physical
+address 0, virtual address @code{PHYS_BASE} + @t{0x1234} access
 physical address @t{0x1234}, and so on up to the size of the machine's
 physical memory.
 
@@ -442,8 +442,8 @@ static inline bool put_user (uint8_t *udst, uint8_t byte) {
 
 Each of these functions assumes that the user address has already been
 verified to be below @code{PHYS_BASE}.  They also assume that you've
-modified @func{page_fault} so that a page fault in the kernel causes
-@code{eax} to be set to 0 and its former value copied into @code{eip}.
+modified @func{page_fault} so that a page fault in the kernel merely sets
+@code{eax} to 0 and copies its former value into @code{eip}.
 
 @node Project 2 Suggested Order of Implementation
 @section Suggested Order of Implementation
@@ -453,7 +453,7 @@ parallel:
 
 @itemize
 @item
-Argument passing (@pxref{Argument Passing}).  Every user programs will
+Argument passing (@pxref{Argument Passing}).  Every user program will
 page fault immediately until argument passing is implemented.
 
 For now, you may simply wish to change
@@ -661,8 +661,12 @@ when the process exits or is terminated.
 
 File descriptors numbered 0 and 1 are reserved for the console: fd 0
 is standard input (@code{stdin}), fd 1 is standard output
-(@code{stdout}).  These special file descriptors are valid as system
-call arguments only as explicitly described below.
+(@code{stdout}).  The @code{open} system call will never return either
+of these file descriptors, which are valid as system call arguments only
+as explicitly described below.
+
+Each process has an independent set of file descriptors.  File
+descriptors are not inherited by child processes.
 
 Consider implementing this function in terms of @func{filesys_open}.
 @end deftypefn