xv6/sysfile.c

//
// File-system system calls.
// Mostly argument checking, since we don't trust
// user code, and calls into file.c and fs.c.
//

#include "types.h"
#include "defs.h"
#include "param.h"
#include "stat.h"
#include "mmu.h"
#include "proc.h"
#include "fs.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "file.h"
#include "fcntl.h"

// Fetch the nth word-sized system call argument as a file descriptor
// and return both the descriptor and the corresponding struct file.
static int argfd(int n, int *pfd, struct file **pf) {
    int fd;
    struct file *f;

    if (argint(n, &fd) < 0) {
        return -1;
    }
    if (fd < 0 || fd >= NOFILE || (f = myproc()->ofile[fd]) == 0) {
        return -1;
    }
    if (pfd) {
        *pfd = fd;
    }
    if (pf) {
        *pf = f;
    }
    return 0;
}

// Allocate a file descriptor for the given file.
// Takes over file reference from caller on success.
static int fdalloc(struct file *f) {
    int fd;
    struct proc *curproc = myproc();

    for (fd = 0; fd < NOFILE; fd++) {
        if (curproc->ofile[fd] == 0) {
            curproc->ofile[fd] = f;
            return fd;
        }
    }
    return -1;
}

int sys_dup(void) {
    struct file *f;
    int fd;

    if (argfd(0, 0, &f) < 0) {
        return -1;
    }
    if ((fd = fdalloc(f)) < 0) {
        return -1;
    }
    filedup(f);
    return fd;
}

int sys_read(void) {
    struct file *f;
    int n;
    char *p;

    if (argfd(0, 0, &f) < 0 || argint(2, &n) < 0 || argptr(1, &p, n) < 0) {
        return -1;
    }
    return fileread(f, p, n);
}

int sys_write(void) {
    struct file *f;
    int n;
    char *p;

    if (argfd(0, 0, &f) < 0 || argint(2, &n) < 0 || argptr(1, &p, n) < 0) {
        return -1;
    }
    return filewrite(f, p, n);
}

int sys_close(void) {
    int fd;
    struct file *f;

    if (argfd(0, &fd, &f) < 0) {
        return -1;
    }
    myproc()->ofile[fd] = 0;
    fileclose(f);
    return 0;
}

int sys_fstat(void) {
    struct file *f;
    struct stat *st;

    if (argfd(0, 0, &f) < 0 || argptr(1, (void*)&st, sizeof(*st)) < 0) {
        return -1;
    }
    return filestat(f, st);
}

void cleanupsyslink(struct inode * ip) {
    ilock(ip);
    ip->nlink--;
    iupdate(ip);
    iunlockput(ip);
    end_op();
}

// Create the path new as a link to the same inode as old.
int sys_link(void) {
    char name[DIRSIZ], *new, *old;
    struct inode *dp, *ip;

    if (argstr(0, &old) < 0 || argstr(1, &new) < 0) {
        return -1;
    }

    begin_op();
    if ((ip = namei(old)) == 0) {
        end_op();
        return -1;
    }

    ilock(ip);
    if (ip->type == T_DIR) {
        iunlockput(ip);
        end_op();
        return -1;
    }

    ip->nlink++;
    iupdate(ip);
    iunlock(ip);

    if ((dp = nameiparent(new, name)) == 0) {
        cleanupsyslink(ip);
        return -1;
    }
    ilock(dp);
    if (dp->dev != ip->dev || dirlink(dp, name, ip->inum) < 0) {
        iunlockput(dp);
        cleanupsyslink(ip);
        return -1;
    }
    iunlockput(dp);
    iput(ip);

    end_op();

    return 0;
}

// Is the directory dp empty except for "." and ".." ?
static int isdirempty(struct inode *dp) {
    int off;
    struct dirent de;

    for (off = 2 * sizeof(de); off < dp->size; off += sizeof(de)) {
        if (readi(dp, (char*)&de, off, sizeof(de)) != sizeof(de)) {
            panic("isdirempty: readi");
        }
        if (de.inum != 0) {
            return 0;
        }
    }
    return 1;
}


int sys_unlink(void) {
    struct inode *ip, *dp;
    struct dirent de;
    char name[DIRSIZ], *path;
    uint off;

    if (argstr(0, &path) < 0) {
        return -1;
    }

    begin_op();
    if ((dp = nameiparent(path, name)) == 0) {
        end_op();
        return -1;
    }

    ilock(dp);

    // Cannot unlink "." or "..".
    if (namecmp(name, ".") == 0 || namecmp(name, "..") == 0) {
        iunlockput(dp);
        end_op();
        return -1;       
    }

    if ((ip = dirlookup(dp, name, &off)) == 0) {
        iunlockput(dp);
        end_op();
        return -1;       
    }
    ilock(ip);

    if (ip->nlink < 1) {
        panic("unlink: nlink < 1");
    }
    if (ip->type == T_DIR && !isdirempty(ip)) {
        iunlockput(ip);
        iunlockput(dp);
        end_op();
        return -1;       
    }

    memset(&de, 0, sizeof(de));
    if (writei(dp, (char*)&de, off, sizeof(de)) != sizeof(de)) {
        panic("unlink: writei");
    }
    if (ip->type == T_DIR) {
        dp->nlink--;
        iupdate(dp);
    }
    iunlockput(dp);

    ip->nlink--;
    iupdate(ip);
    iunlockput(ip);

    end_op();

    return 0;
}

static struct inode* create(char *path, short type, short major, short minor)  {
    struct inode *ip, *dp;
    char name[DIRSIZ];

    if ((dp = nameiparent(path, name)) == 0) {
        return 0;
    }
    ilock(dp);

    if ((ip = dirlookup(dp, name, 0)) != 0) {
        iunlockput(dp);
        ilock(ip);
        if (type == T_FILE && ip->type == T_FILE) {
            return ip;
        }
        iunlockput(ip);
        return 0;
    }

    if ((ip = ialloc(dp->dev, type)) == 0) {
        panic("create: ialloc");
    }

    ilock(ip);
    ip->major = major;
    ip->minor = minor;
    ip->nlink = 1;
    iupdate(ip);

    if (type == T_DIR) { // Create . and .. entries.
        dp->nlink++;  // for ".."
        iupdate(dp);
        // No ip->nlink++ for ".": avoid cyclic ref count.
        if (dirlink(ip, ".", ip->inum) < 0 || dirlink(ip, "..", dp->inum) < 0) {
            panic("create dots");
        }
    }

    if (dirlink(dp, name, ip->inum) < 0) {
        panic("create: dirlink");
    }

    iunlockput(dp);

    return ip;
}

int sys_open(void) {
    char *path;
    int fd, omode;
    struct file *f;
    struct inode *ip;

    if (argstr(0, &path) < 0 || argint(1, &omode) < 0) {
        return -1;
    }

    begin_op();

    if (omode & O_CREATE) {
        ip = create(path, T_FILE, 0, 0);
        if (ip == 0) {
            end_op();
            return -1;
        }
    }
    else {
        if ((ip = namei(path)) == 0) {
            end_op();
            return -1;
        }
        ilock(ip);
        if (ip->type == T_DIR && omode != O_RDONLY) {
            iunlockput(ip);
            end_op();
            return -1;
        }
    }

    if ((f = filealloc()) == 0 || (fd = fdalloc(f)) < 0) {
        if (f) {
            fileclose(f);
        }
        iunlockput(ip);
        end_op();
        return -1;
    }
    iunlock(ip);
    end_op();

    f->type = FD_INODE;
    f->ip = ip;
    f->off = 0;
    f->readable = !(omode & O_WRONLY);
    f->writable = (omode & O_WRONLY) || (omode & O_RDWR);
    return fd;
}

int sys_mkdir(void) {
    char *path;
    struct inode *ip;

    begin_op();
    if (argstr(0, &path) < 0 || (ip = create(path, T_DIR, 0, 0)) == 0) {
        end_op();
        return -1;
    }
    iunlockput(ip);
    end_op();
    return 0;
}

int sys_mknod(void) {
    struct inode *ip;
    char *path;
    int major, minor;

    begin_op();
    if ((argstr(0, &path)) < 0 ||
        argint(1, &major) < 0 ||
        argint(2, &minor) < 0 ||
        (ip = create(path, T_DEV, major, minor)) == 0) {
        end_op();
        return -1;
    }
    iunlockput(ip);
    end_op();
    return 0;
}

int sys_chdir(void) {
    char *path;
    struct inode *ip;
    struct proc *curproc = myproc();

    begin_op();
    if (argstr(0, &path) < 0 || (ip = namei(path)) == 0) {
        end_op();
        return -1;
    }
    ilock(ip);
    if (ip->type != T_DIR) {
        iunlockput(ip);
        end_op();
        return -1;
    }
    iunlock(ip);
    iput(curproc->cwd);
    end_op();
    curproc->cwd = ip;
    return 0;
}

int sys_exec(void) {
    char *path, *argv[MAXARG];
    int i;
    uint uargv, uarg;

    if (argstr(0, &path) < 0 || argint(1, (int*)&uargv) < 0) {
        return -1;
    }
    memset(argv, 0, sizeof(argv));
    for (i = 0;; i++) {
        if (i >= NELEM(argv)) {
            return -1;
        }
        if (fetchint(uargv + 4 * i, (int*)&uarg) < 0) {
            return -1;
        }
        if (uarg == 0) {
            argv[i] = 0;
            break;
        }
        if (fetchstr(uarg, &argv[i]) < 0) {
            return -1;
        }
    }
    return exec(path, argv);
}

int sys_pipe(void) {
    int *fd;
    struct file *rf, *wf;
    int fd0, fd1;

    if (argptr(0, (void*)&fd, 2 * sizeof(fd[0])) < 0) {
        return -1;
    }
    if (pipealloc(&rf, &wf) < 0) {
        return -1;
    }
    fd0 = -1;
    if ((fd0 = fdalloc(rf)) < 0 || (fd1 = fdalloc(wf)) < 0) {
        if (fd0 >= 0) {
            myproc()->ofile[fd0] = 0;
        }
        fileclose(rf);
        fileclose(wf);
        return -1;
    }
    fd[0] = fd0;
    fd[1] = fd1;
    return 0;
}

int sys_getch(void) {
    return consoleget();
}