readdir and getdents interfaces -- number of bytes read? - c

Question

I'm working on Cygwin, which does not implement getdents, nor getdirentries.
The code I'm working on relies on knowing the number of bytes read, which is the return of these calls. All I seem to have is readdir.
Man pages are lacking in Cygwin. Any ideas, or existing documentation, on how to make these interfaces compatible, or how to get the number of bytes read from readdir?
Cygwin's struct dirent, in case it's relevant:
struct dirent
{
uint32_t __d_version; /* Used internally */
ino_t d_ino;
unsigned char d_type;
unsigned char __d_unused1[3];
__uint32_t __d_internal1;
char d_name[NAME_MAX + 1];
};
EDIT
The code that uses getdents is in function readdir (see the link for full file):
static int
mygetdents(int fd, struct dirent *buf, int n) {
return syscall (getdents, fd, (void*) buf, n);
}
long
dirread(int fd, Dir **dp)
{
char *buf;
struct stat st;
int n;
*dp = 0;
if(fstat(fd, &st) < 0)
return -1;
if(st.st_blksize < 8192)
st.st_blksize = 8192;
buf = malloc(st.st_blksize);
if(buf == nil)
return -1;
n = mygetdents(fd, (void*)buf, st.st_blksize);
if(n < 0){
free(buf);
return -1;
}
n = dirpackage(fd, buf, n, dp);
free(buf);
return n;
}
static int
dirpackage(int fd, char *buf, int n, Dir **dp)
{
int oldwd;
char *p, *str, *estr;
int i, nstr, m;
struct dirent *de;
struct stat st, lst;
Dir *d;
n = countde(buf, n);
if(n <= 0)
return n;
if((oldwd = open(".", O_RDONLY)) < 0)
return -1;
if(fchdir(fd) < 0)
return -1;
p = buf;
nstr = 0;
for(i=0; i<n; i++){
de = (struct dirent*)p;
memset(&lst, 0, sizeof lst);
if(de->d_name[0] == 0)
/* nothing */ {}
else if(lstat(de->d_name, &lst) < 0)
de->d_name[0] = 0;
else{
st = lst;
if(S_ISLNK(lst.st_mode))
stat(de->d_name, &st);
nstr += _p9dir(&lst, &st, de->d_name, nil, nil, nil);
}
p += de->d_reclen;
}
d = malloc(sizeof(Dir)*n+nstr);
if(d == nil){
fchdir(oldwd);
close(oldwd);
return -1;
}
str = (char*)&d[n];
estr = str+nstr;
p = buf;
m = 0;
for(i=0; i<n; i++){
de = (struct dirent*)p;
if(de->d_name[0] != 0 && lstat(de->d_name, &lst) >= 0){
st = lst;
if((lst.st_mode&S_IFMT) == S_IFLNK)
stat(de->d_name, &st);
_p9dir(&lst, &st, de->d_name, &d[m++], &str, estr);
}
p += de->d_reclen;
}
fchdir(oldwd);
close(oldwd);
*dp = d;
return m;
}
static int
countde(char *p, int n)
{
char *e;
int m;
struct dirent *de;
e = p+n;
m = 0;
while(p < e){
de = (struct dirent*)p;
if(de->d_reclen <= 4+2+2+1 || p+de->d_reclen > e)
break;
if(de->d_name[0]=='.' && de->d_name[1]==0)
de->d_name[0] = 0;
else if(de->d_name[0]=='.' && de->d_name[1]=='.' && de->d_name[2]==0)
de->d_name[0] = 0;
m++;
p += de->d_reclen;
}
return m;
}
I haven't made sense of dirpackage yet, but I think I may get around that detail if I could get the return of getdents in another way.

Answer 1

From the link you posted to the dirpackage method:
for(i=0; i<n; i++){
de = (struct dirent*)p;
memset(&lst, 0, sizeof lst);
if(de->d_name[0] == 0)
/* nothing */ {}
else if(lstat(de->d_name, &lst) < 0)
de->d_name[0] = 0;
else{
st = lst;
if(S_ISLNK(lst.st_mode))
stat(de->d_name, &st);
nstr += _p9dir(&lst, &st, de->d_name, nil, nil, nil);
}
p += de->d_reclen;
}
Here n comes from:
n = countde(buf, n);
... where the original value of n is supplied from the return of the getdents syscall. The name countde probably stands for "count directory entries".
As you can see from the loop, the return from countde represents the number of entries returned by the getdents call. Each iteration through the loop processes one directory entry (de = (struct dirent*)p;) and then finds the next one (p += de->d_reclen;).
That should be pretty straight-forward to translate to using readdir, since it only ever returns one entry.