Problem $2(50$ points$)$

Modify the rio$\_$read$()$ function to treat the rio$\_$buf as a circular buffer when the user decides

to do so:

The call to rio$\_$read$()$ must remain the same:

rio$\_$read $($rio$\_$t $*$ rp$,$ char $*$ usrbuf, size$\_$t $n)$

When the circular use is enabled, rio$\_$read$()$ copies bytes from rio$\_$buf to the caller's

usrbuf. When the last byte from rio$\_$buf has been given to the user, the NEXT CALL to

rio$\_$read$()$ copies bytes from the beginning of rio$\_$buf instead of refilling rio$\_$buf with a

read from the file.

Write a function rio$\_$circular $($rio$\_$t $*$ rp$,$ int $v)$ to select circular use or not:

'rio$\_$circular' $($rp$,\frac{?}{\text{b}\text{a}\text{r}}(1))$ enables circular use

rio$\_$circular $(rp,0)$ disables circular use

Make the necessary modifications to rio$\_$read$()$ and elsewhere but do not change its

arguments.

For Reference

int open$($const char $*$pathname$,$ int flags, mode$\_$t mode$)$;

ssize$\_$t read$($int fd$,$ void $*$buf$,$ size$\_$t count$)$;

off$\_$t Iseek$($int fd$,$ off$\_$t offset, int whence$)$;

O$\_$APPEND enables append mode: all write operations write the data the end the file,

extending it$,$ regardless of the $C$

#define RIO$\_$BUFSIZE $8192$

typedef str$$ct $\{$

int rio$\_$fd;

int rio$\_$cnt;

char $*$rio$\_$bufptr; r

char rio$\_$buf $[$RIO$\_$BUFSIZE$]$;

$\}$ rio$\_$t;

void rio$\_$readinitb$($rio$\_$t $*$ rp$,$ int fd$)$

$1$

rp$->$rio$\_$fd $=$ fd;

rp$-$rio$\_$cnt $=0$;

rp$->$rio$\_$bufptr $=$ rp$->$rio$\_$buf;

$\}$

ssize$\_$t rio$\_$read $($rio$\_$t $*$ rp$,$ char $*$ usrbuf, size$\_$t $n)$

$1$

int cnt;

if $($rp$->$rio$\_$cnt $=0)$

$1$

$1^{**}$ refill if buf is empty $*/$

rp$->$rio$\_$cnt $=$ read$($rp$->$rio$\_$fd$,$ rp$->$rio$\_$buf, sizeof $($rp$->$rio$\_$buf$))$;

if $(rp->$rio$\_$cnt $<mn\; id="EditorElement\_1235164">0</mn><mtext\; id="EditorElement\_1235134"></mtext><mi\; id="EditorElement\_1235135">)</mi>$ return $-1$ ;

else if $(r{p}^{-}-$riocnt$=0)$ return $0$;$I^{***EOF}**\frac{*}{?}$

else rp$->$rio$\_$bufptr $=$ rp$->$rio$\_$buf; $\frac{?}{?}**$ reset buffer ptr $**\frac{*}{?}$

$\}$

$/*$ Copy min$(n,$ rp$->$rio$\_$cnt$)$ bytes from internal buf to user buf $**\frac{*}{?}$

cnt $=n$;

if $(rp$ rio$\_$cnt $=r{p}_p+=-=$ Modify the rio $\_$read$()$ function to treat the rio$\_$buf as a circular buffer when the user decides to do so:

$$ The call to rio read$()$ must remain the same:

$$ rio read $($riot $*$ rp$,$ char $*$ usrbuf, size$\_$t n$)$

$$ When the circular use is enabled, rio$\_$read$()$ copies bytes from rio$\_$buf to the caller's usrbuf. When the last byte from rio$\_$buf has been given to the user, the NEXT CALL to rio$\_$read$()$ copies bytes from the beginning of rio$\_$buf instead of refilling rio$\_$buf with a read from the file.

Write a function rio$\_$circular $($rio$\_$t $*$ rp$,$ int v$)$ to select circular use or not:

$$

W$"$rio circular $($rp$,1)$ enables circular use

$$ rio circular $($rp$,$O$)$ disables circular use

$$Make the necessary modifications to rio$\_$read$()$ and elsewhere but do not change its arguments.