/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software donated to Berkeley by
 * Jan-Simon Pendry.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * /dev/fd Filesystem
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/capsicum.h>
#include <sys/conf.h>
#include <sys/dirent.h>
#include <sys/filedesc.h>
#include <sys/kernel.h> /* boottime */
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/malloc.h>
#include <sys/file.h>   /* Must come after sys/malloc.h */
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/proc.h>
#include <sys/stat.h>
#include <sys/syscallsubr.h>
#include <sys/unistd.h>
#include <sys/vnode.h>

#include <fs/fdescfs/fdesc.h>

#define NFDCACHE 4
#define FD_NHASH(ix) \
        (&fdhashtbl[(ix) & fdhash])
static LIST_HEAD(fdhashhead, fdescnode) *fdhashtbl;
static u_long fdhash;

struct mtx fdesc_hashmtx;

static vop_getattr_t    fdesc_getattr;
static vop_lookup_t     fdesc_lookup;
static vop_open_t       fdesc_open;
static vop_pathconf_t   fdesc_pathconf;
static vop_readdir_t    fdesc_readdir;
static vop_readlink_t   fdesc_readlink;
static vop_reclaim_t    fdesc_reclaim;
static vop_setattr_t    fdesc_setattr;

static struct vop_vector fdesc_vnodeops = {
        .vop_default =          &default_vnodeops,

        .vop_access =           VOP_NULL,
        .vop_getattr =          fdesc_getattr,
        .vop_lookup =           fdesc_lookup,
        .vop_open =             fdesc_open,
        .vop_pathconf =         fdesc_pathconf,
        .vop_readdir =          fdesc_readdir,
        .vop_readlink =         fdesc_readlink,
        .vop_reclaim =          fdesc_reclaim,
        .vop_setattr =          fdesc_setattr,
};
VFS_VOP_VECTOR_REGISTER(fdesc_vnodeops);

static void fdesc_remove_entry(struct fdescnode *);

/*
 * Initialise cache headers
 */
int
fdesc_init(struct vfsconf *vfsp)
{

        mtx_init(&fdesc_hashmtx, "fdescfs_hash", NULL, MTX_DEF);
        fdhashtbl = hashinit(NFDCACHE, M_CACHE, &fdhash);
        return (0);
}

/*
 * Uninit ready for unload.
 */
int
fdesc_uninit(struct vfsconf *vfsp)
{

        hashdestroy(fdhashtbl, M_CACHE, fdhash);
        mtx_destroy(&fdesc_hashmtx);
        return (0);
}

/*
 * Remove an entry from the hash if it exists.
 */
static void
fdesc_remove_entry(struct fdescnode *fd)
{
        struct fdhashhead *fc;
        struct fdescnode *fd2;

        fc = FD_NHASH(fd->fd_ix);
        mtx_lock(&fdesc_hashmtx);
        LIST_FOREACH(fd2, fc, fd_hash) {
                if (fd == fd2) {
                        LIST_REMOVE(fd, fd_hash);
                        break;
                }
        }
        mtx_unlock(&fdesc_hashmtx);
}

int
fdesc_allocvp(fdntype ftype, unsigned fd_fd, int ix, struct mount *mp,
    struct vnode **vpp)
{
        struct fdescmount *fmp;
        struct fdhashhead *fc;
        struct fdescnode *fd, *fd2;
        struct vnode *vp, *vp2;
        enum vgetstate vgs;
        int error;

        fc = FD_NHASH(ix);
loop:
        mtx_lock(&fdesc_hashmtx);
        /*
         * If a forced unmount is progressing, we need to drop it. The flags are
         * protected by the hashmtx.
         */
        fmp = mp->mnt_data;
        if (fmp == NULL || fmp->flags & FMNT_UNMOUNTF) {
                mtx_unlock(&fdesc_hashmtx);
                return (-1);
        }

        LIST_FOREACH(fd, fc, fd_hash) {
                if (fd->fd_ix == ix && fd->fd_vnode->v_mount == mp) {
                        /* Get reference to vnode in case it's being free'd */
                        vp = fd->fd_vnode;
                        vgs = vget_prep(vp);
                        mtx_unlock(&fdesc_hashmtx);
                        if (vget_finish(vp, LK_EXCLUSIVE, vgs) != 0)
                                goto loop;
                        *vpp = vp;
                        return (0);
                }
        }
        mtx_unlock(&fdesc_hashmtx);

        fd = malloc(sizeof(struct fdescnode), M_TEMP, M_WAITOK);

        error = getnewvnode("fdescfs", mp, &fdesc_vnodeops, &vp);
        if (error) {
                free(fd, M_TEMP);
                return (error);
        }
        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
        vp->v_data = fd;
        fd->fd_vnode = vp;
        fd->fd_type = ftype;
        fd->fd_fd = fd_fd;
        fd->fd_ix = ix;
        if (ftype == Fdesc) {
                if ((fmp->flags & FMNT_RDLNKF) != 0)
                        vp->v_type = VLNK;
                else if ((fmp->flags & FMNT_LINRDLNKF) != 0)
                        vp->v_vflag |= VV_READLINK;
        }
        error = insmntque1(vp, mp);
        if (error != 0) {
                vgone(vp);
                vput(vp);
                *vpp = NULL;
                return (error);
        }

        /* Make sure that someone didn't beat us when inserting the vnode. */
        mtx_lock(&fdesc_hashmtx);
        /*
         * If a forced unmount is progressing, we need to drop it. The flags are
         * protected by the hashmtx.
         */
        fmp = mp->mnt_data;
        if (fmp == NULL || fmp->flags & FMNT_UNMOUNTF) {
                mtx_unlock(&fdesc_hashmtx);
                vgone(vp);
                vput(vp);
                *vpp = NULL;
                return (-1);
        }

        LIST_FOREACH(fd2, fc, fd_hash) {
                if (fd2->fd_ix == ix && fd2->fd_vnode->v_mount == mp) {
                        /* Get reference to vnode in case it's being free'd */
                        vp2 = fd2->fd_vnode;
                        vgs = vget_prep(vp2);
                        mtx_unlock(&fdesc_hashmtx);
                        error = vget_finish(vp2, LK_EXCLUSIVE, vgs);
                        /* Someone beat us, dec use count and wait for reclaim */
                        vgone(vp);
                        vput(vp);
                        /* If we didn't get it, return no vnode. */
                        if (error)
                                vp2 = NULL;
                        *vpp = vp2;
                        return (error);
                }
        }

        /* If we came here, we can insert it safely. */
        LIST_INSERT_HEAD(fc, fd, fd_hash);
        mtx_unlock(&fdesc_hashmtx);
        vn_set_state(vp, VSTATE_CONSTRUCTED);
        *vpp = vp;
        return (0);
}

struct fdesc_get_ino_args {
        fdntype ftype;
        unsigned fd_fd;
        int ix;
        struct file *fp;
        struct thread *td;
        bool fdropped;
};

static int
fdesc_get_ino_alloc(struct mount *mp, void *arg, int lkflags,
    struct vnode **rvp)
{
        struct fdesc_get_ino_args *a;
        struct fdescmount *fdm;
        struct vnode *vp;
        int error;

        a = arg;
        fdm = VFSTOFDESC(mp);
        if ((fdm->flags & FMNT_NODUP) != 0 && a->fp->f_type == DTYPE_VNODE) {
                vp = a->fp->f_vnode;
                vget(vp, lkflags | LK_RETRY);
                *rvp = vp;
                error = 0;
        } else {
                error = fdesc_allocvp(a->ftype, a->fd_fd, a->ix, mp, rvp);
        }
        fdrop(a->fp, a->td);
        a->fdropped = true;
        return (error);
}

/*
 * vp is the current namei directory
 * ndp is the name to locate in that directory...
 */
static int
fdesc_lookup(struct vop_lookup_args *ap)
{
        struct vnode **vpp = ap->a_vpp;
        struct vnode *dvp = ap->a_dvp;
        struct componentname *cnp = ap->a_cnp;
        char *pname = cnp->cn_nameptr;
        struct thread *td = curthread;
        struct file *fp;
        struct fdesc_get_ino_args arg;
        int nlen = cnp->cn_namelen;
        u_int fd, fd1;
        int error;
        struct vnode *fvp;

        if ((cnp->cn_flags & ISLASTCN) &&
            (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
                error = EROFS;
                goto bad;
        }

        if (cnp->cn_namelen == 1 && *pname == '.') {
                *vpp = dvp;
                vref(dvp);
                return (0);
        }

        if (VTOFDESC(dvp)->fd_type != Froot) {
                error = ENOTDIR;
                goto bad;
        }

        fd = 0;
        /* the only time a leading 0 is acceptable is if it's "0" */
        if (*pname == '0' && nlen != 1) {
                error = ENOENT;
                goto bad;
        }
        while (nlen--) {
                if (*pname < '0' || *pname > '9') {
                        error = ENOENT;
                        goto bad;
                }
                fd1 = 10 * fd + *pname++ - '0';
                if (fd1 < fd) {
                        error = ENOENT;
                        goto bad;
                }
                fd = fd1;
        }

        /*
         * No rights to check since 'fp' isn't actually used.
         */
        if ((error = fget(td, fd, &cap_no_rights, &fp)) != 0)
                goto bad;

        /*
         * Make sure we do not deadlock looking up the dvp itself.
         *
         * Unlock our root node (dvp) when doing this, since we might
         * deadlock since the vnode might be locked by another thread
         * and the root vnode lock will be obtained afterwards (in case
         * we're looking up the fd of the root vnode), which will be the
         * opposite lock order.
         */
        arg.ftype = Fdesc;
        arg.fd_fd = fd;
        arg.ix = FD_DESC + fd;
        arg.fp = fp;
        arg.td = td;
        arg.fdropped = false;
        error = vn_vget_ino_gen(dvp, fdesc_get_ino_alloc, &arg,
            LK_EXCLUSIVE, &fvp);

        if (!arg.fdropped) {
                /*
                 * In case we're holding the last reference to the file, the dvp
                 * will be re-acquired.
                 */
                VOP_UNLOCK(dvp);
                fdrop(fp, td);

                vn_lock(dvp, LK_RETRY | LK_EXCLUSIVE);
                fvp = dvp;
                if (error == 0 && VN_IS_DOOMED(dvp))
                        error = ENOENT;
        }

        if (error)
                goto bad;
        *vpp = fvp;
        return (0);

bad:
        *vpp = NULL;
        return (error);
}

static int
fdesc_open(struct vop_open_args *ap)
{
        struct vnode *vp = ap->a_vp;

        if (VTOFDESC(vp)->fd_type == Froot)
                return (0);

        /*
         * XXX Kludge: set td->td_proc->p_dupfd to contain the value of the file
         * descriptor being sought for duplication. The error return ensures
         * that the vnode for this device will be released by vn_open. Open
         * will detect this special error and take the actions in dupfdopen.
         * Other callers of vn_open or VOP_OPEN will simply report the
         * error.
         */
        ap->a_td->td_dupfd = VTOFDESC(vp)->fd_fd;       /* XXX */
        return (ENODEV);
}

static int
fdesc_pathconf(struct vop_pathconf_args *ap)
{
        struct vnode *vp = ap->a_vp;
        int error;

        switch (ap->a_name) {
        case _PC_NAME_MAX:
                *ap->a_retval = NAME_MAX;
                return (0);
        case _PC_LINK_MAX:
                if (VTOFDESC(vp)->fd_type == Froot)
                        *ap->a_retval = 2;
                else
                        *ap->a_retval = 1;
                return (0);
        default:
                if (VTOFDESC(vp)->fd_type == Froot)
                        return (vop_stdpathconf(ap));
                vref(vp);
                VOP_UNLOCK(vp);
                error = kern_fpathconf(curthread, VTOFDESC(vp)->fd_fd,
                    ap->a_name, ap->a_retval);
                vn_lock(vp, LK_SHARED | LK_RETRY);
                vunref(vp);
                return (error);
        }
}

static int
fdesc_getattr(struct vop_getattr_args *ap)
{
        struct vnode *vp = ap->a_vp;
        struct vattr *vap = ap->a_vap;
        struct timeval boottime;

        getboottime(&boottime);
        vap->va_mode = S_IRUSR|S_IXUSR|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH;
        vap->va_fileid = VTOFDESC(vp)->fd_ix;
        vap->va_uid = 0;
        vap->va_gid = 0;
        vap->va_blocksize = DEV_BSIZE;
        vap->va_atime.tv_sec = boottime.tv_sec;
        vap->va_atime.tv_nsec = 0;
        vap->va_mtime = vap->va_atime;
        vap->va_ctime = vap->va_mtime;
        vap->va_gen = 0;
        vap->va_flags = 0;
        vap->va_bytes = 0;
        vap->va_filerev = 0;

        switch (VTOFDESC(vp)->fd_type) {
        case Froot:
                vap->va_type = VDIR;
                vap->va_nlink = 2;
                vap->va_size = DEV_BSIZE;
                vap->va_rdev = NODEV;
                break;

        case Fdesc:
                vap->va_type = (VFSTOFDESC(vp->v_mount)->flags &
                    (FMNT_RDLNKF | FMNT_LINRDLNKF)) == 0 ? VCHR : VLNK;
                vap->va_nlink = 1;
                vap->va_size = 0;
                vap->va_rdev = makedev(0, vap->va_fileid);
                break;

        default:
                panic("fdesc_getattr");
                break;
        }

        vp->v_type = vap->va_type;
        return (0);
}

static int
fdesc_setattr(struct vop_setattr_args *ap)
{
        struct vattr *vap = ap->a_vap;
        struct vnode *vp;
        struct mount *mp;
        struct file *fp;
        struct thread *td = curthread;
        cap_rights_t rights;
        unsigned fd;
        int error;

        /*
         * Can't mess with the root vnode
         */
        if (VTOFDESC(ap->a_vp)->fd_type == Froot)
                return (EACCES);

        fd = VTOFDESC(ap->a_vp)->fd_fd;

        /*
         * Allow setattr where there is an underlying vnode.
         * For O_PATH descriptors, disallow truncate.
         */
        if (vap->va_size != VNOVAL) {
                error = getvnode(td, fd,
                    cap_rights_init_one(&rights, CAP_EXTATTR_SET), &fp);
        } else {
                error = getvnode_path(td, fd,
                    cap_rights_init_one(&rights, CAP_EXTATTR_SET), NULL, &fp);
        }
        if (error) {
                /*
                 * getvnode() returns EINVAL if the file descriptor is not
                 * backed by a vnode.  Silently drop all changes except
                 * chflags(2) in this case.
                 */
                if (error == EINVAL) {
                        if (vap->va_flags != VNOVAL)
                                error = EOPNOTSUPP;
                        else
                                error = 0;
                }
                return (error);
        }
        vp = fp->f_vnode;
        if ((error = vn_start_write(vp, &mp, V_WAIT | V_PCATCH)) == 0) {
                vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
                error = VOP_SETATTR(vp, ap->a_vap, ap->a_cred);
                VOP_UNLOCK(vp);
                vn_finished_write(mp);
        }
        fdrop(fp, td);
        return (error);
}

#define UIO_MX _GENERIC_DIRLEN(10) /* number of symbols in INT_MAX printout */

static int
fdesc_readdir(struct vop_readdir_args *ap)
{
        struct fdescmount *fmp;
        struct uio *uio = ap->a_uio;
        struct filedesc *fdp;
        struct dirent d;
        struct dirent *dp = &d;
        int error, i, off, fcnt;

        if (VTOFDESC(ap->a_vp)->fd_type != Froot)
                panic("fdesc_readdir: not dir");

        fmp = VFSTOFDESC(ap->a_vp->v_mount);
        if (ap->a_ncookies != NULL)
                *ap->a_ncookies = 0;
        if (ap->a_eofflag != NULL)
                *ap->a_eofflag = 0;

        off = (int)uio->uio_offset;
        if (off != uio->uio_offset || off < 0 || (u_int)off % UIO_MX != 0 ||
            uio->uio_resid < UIO_MX)
                return (EINVAL);
        i = (u_int)off / UIO_MX;
        fdp = uio->uio_td->td_proc->p_fd;
        error = 0;

        fcnt = i - 2;           /* The first two nodes are `.' and `..' */

        FILEDESC_SLOCK(fdp);
        while (uio->uio_resid >= UIO_MX) {
                if (i >= fdp->fd_nfiles + 2) {
                        if (ap->a_eofflag != NULL)
                                *ap->a_eofflag = 1;
                        break;
                }
                bzero((caddr_t)dp, UIO_MX);
                switch (i) {
                case 0: /* `.' */
                case 1: /* `..' */
                        dp->d_fileno = i + FD_ROOT;
                        dp->d_namlen = i + 1;
                        dp->d_reclen = UIO_MX;
                        bcopy("..", dp->d_name, dp->d_namlen);
                        dp->d_type = DT_DIR;
                        dirent_terminate(dp);
                        break;
                default:
                        if (fdp->fd_ofiles[fcnt].fde_file == NULL)
                                break;
                        dp->d_namlen = sprintf(dp->d_name, "%d", fcnt);
                        dp->d_reclen = UIO_MX;
                        dp->d_type = (fmp->flags & (FMNT_RDLNKF |
                            FMNT_LINRDLNKF)) == 0 ? DT_CHR : DT_LNK;
                        dp->d_fileno = i + FD_DESC;
                        dirent_terminate(dp);
                        break;
                }
                /* NOTE: d_off is the offset of the *next* entry. */
                dp->d_off = UIO_MX * (i + 1);
                if (dp->d_namlen != 0) {
                        /*
                         * And ship to userland
                         */
                        FILEDESC_SUNLOCK(fdp);
                        error = uiomove(dp, UIO_MX, uio);
                        if (error)
                                goto done;
                        FILEDESC_SLOCK(fdp);
                }
                i++;
                fcnt++;
        }
        FILEDESC_SUNLOCK(fdp);

done:
        uio->uio_offset = i * UIO_MX;
        return (error);
}

static int
fdesc_reclaim(struct vop_reclaim_args *ap)
{
        struct vnode *vp;
        struct fdescnode *fd;

        vp = ap->a_vp;
        fd = VTOFDESC(vp);
        fdesc_remove_entry(fd);
        free(vp->v_data, M_TEMP);
        vp->v_data = NULL;
        return (0);
}

static int
fdesc_readlink(struct vop_readlink_args *va)
{
        struct vnode *vp, *vn;
        struct thread *td;
        struct uio *uio;
        struct file *fp;
        char *freepath, *fullpath;
        size_t pathlen;
        int lockflags, fd_fd;
        int error;

        freepath = NULL;
        vn = va->a_vp;
        if (VTOFDESC(vn)->fd_type != Fdesc)
                panic("fdesc_readlink: not fdescfs link");
        fd_fd = ((struct fdescnode *)vn->v_data)->fd_fd;
        lockflags = VOP_ISLOCKED(vn);
        VOP_UNLOCK(vn);

        td = curthread;
        error = fget_cap(td, fd_fd, &cap_no_rights, NULL, &fp, NULL);
        if (error != 0)
                goto out;

        switch (fp->f_type) {
        case DTYPE_VNODE:
                vp = fp->f_vnode;
                error = vn_fullpath(vp, &fullpath, &freepath);
                break;
        default:
                fullpath = "anon_inode:[unknown]";
                break;
        }
        if (error == 0) {
                uio = va->a_uio;
                pathlen = strlen(fullpath);
                error = uiomove(fullpath, pathlen, uio);
        }
        if (freepath != NULL)
                free(freepath, M_TEMP);
        fdrop(fp, td);

out:
        vn_lock(vn, lockflags | LK_RETRY);
        return (error);
}