UNIX文件系统接口理解——简版ls -s实

#include <stdio.h>
#include <string.h>
#include "syscalls.h"
#include <fcntl.h> /* flags for read and write */
#include <sys/types.h> /* typedefs */
#include <sys/stat.h> /* structure returned by stat */
#include "dirent.h"

void fsize(char *)
/* print file name */
main(int argc, char **argv)
{
    if (argc == 1) /* default: current directory */
        fsize(".");
    else
        while (--argc > 0)
            fsize(*++argv);
    return 0;
}

int stat(char *, struct stat *);
void dirwalk(char *, void (*fcn)(char *));

/* fsize: print the name of file "name" */
void fsize(char *name)
{
    struct stat stbuf;
    if (stat(name, &stbuf) == -1) {
        fprintf(stderr, "fsize: can‘t access %s\n", name);
        return;
    }
    if ((stbuf.st_mode & S_IFMT) == S_IFDIR)
        dirwalk(name, fsize);
    printf("%8ld %s\n", stbuf.st_size, name);
}

#define MAX_PATH 1024
/* dirwalk: apply fcn to all files in dir */
void dirwalk(char *dir, void (*fcn)(char *))
{
    char name[MAX_PATH];
    Dirent *dp;
    DIR *dfd;
    if ((dfd = opendir(dir)) == NULL) {
        fprintf(stderr, "dirwalk: can‘t open %s\n", dir);
        return;
    }
    while ((dp = readdir(dfd)) != NULL) {
        if (strcmp(dp->name, ".") == 0 || strcmp(dp->name, ".."))
            continue; /* skip self and parent */                            
        if (strlen(dir)+strlen(dp->name)+2 > sizeof(name))
            fprintf(stderr, "dirwalk: name %s %s too long\n", dir, dp->name);
        else {
            sprintf(name, "%s/%s", dir, dp->name);
            (*fcn)(name);
        }
    }
    closedir(dfd);
}
说明:
    Each call to readdir returns a pointer to information for the next file, or NULL when there are
    no files left. Each directory always contains entries for itself, called "." , and its parent, ".." ;
    these must be skipped, or the program will loop forever.

//---------------------以下为系统针对性实现(Version 7 and System V UNIX systems)
#ifndef DIRSIZ
#define DIRSIZ 14
#endif
typedef struct direct { /* directory entry */               ;             
    ino_t d_ino; /* inode number */                            
    char d_name[DIRSIZ]; /* long name does not have ‘\0‘ */
} DIR;

int fstat(int fd, struct stat *);

/* opendir: open a directory for readdir calls */
DIR *opendir(char *dirname)
{
    int fd;
    struct stat stbuf;
    DIR *dp;
    if ((fd = open(dirname, O_RDONLY, 0)) == -1
        || fstat(fd, &stbuf) == -1
        || (stbuf.st_mode & S_IFMT) != S_IFDIR
        || (dp = (DIR *) malloc(sizeof(DIR))) == NULL)
            return NULL;
    dp->fd = fd;
    return dp;
}
说明:
    opendir opens the directory, verifies that
    fstat , which is like stat except that it
    the file is a directory (this time by the system call
    applies to a file descriptor), allocates a directory
    structure, and records the information:

/* closedir: close directory opened by opendir */
void closedir(DIR *dp)
{
    if (dp) {
        close(dp->fd);
        free(dp);
    }
}

#include <sys/dir.h> /* local directory structure */

/* readdir: read directory entries in sequence */
Dirent *readdir(DIR *dp)
{
    struct direct dirbuf; /* local directory structure */
    static Dirent d; /* return: portable structure */                            
    while (read(dp->fd, (char *) &dirbuf, sizeof(dirbuf)) == sizeof(dirbuf)) {
        if (dirbuf.d_ino == 0) /* slot not in use */
            continue;
        d.ino = dirbuf.d_ino;
        strncpy(d.name, dirbuf.d_name, DIRSIZ);
        d.name[DIRSIZ] = ‘\0‘; /* ensure termination */
        return &d;
    }
    return NULL;
}