zircon/system/ulib/memfs/vmo.cpp

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <inttypes.h>
#include <fcntl.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>

#include <fbl/algorithm.h>
#include <fbl/alloc_checker.h>
#include <fbl/ref_ptr.h>
#include <fbl/unique_ptr.h>
#include <lib/fdio/vfs.h>
#include <fs/vfs.h>
#include <lib/memfs/cpp/vnode.h>
#include <zircon/device/vfs.h>

#include "dnode.h"

namespace memfs {
namespace {

bool WindowMatchesVMO(zx_handle_t vmo, zx_off_t offset, zx_off_t length) {
    if (offset != 0)
        return false;
    uint64_t size;
    if (zx_vmo_get_size(vmo, &size) < 0)
        return false;
    return size == length;
}

}  // namespace

VnodeVmo::VnodeVmo(Vfs* vfs, zx_handle_t vmo, zx_off_t offset, zx_off_t length)
    : VnodeMemfs(vfs), vmo_(vmo), offset_(offset), length_(length), have_local_clone_(false) {}

VnodeVmo::~VnodeVmo() {
    if (have_local_clone_) {
        zx_handle_close(vmo_);
    }
}

zx_status_t VnodeVmo::ValidateFlags(uint32_t flags) {
    if (flags & ZX_FS_FLAG_DIRECTORY) {
        return ZX_ERR_NOT_DIR;
    }
    if (flags & ZX_FS_RIGHT_WRITABLE) {
        return ZX_ERR_ACCESS_DENIED;
    }
    return ZX_OK;
}

zx_status_t VnodeVmo::GetNodeInfo(uint32_t flags, fuchsia_io_NodeInfo* info) {
    zx_info_handle_basic_t handle_info;
    zx_status_t status = zx_object_get_info(vmo_, ZX_INFO_HANDLE_BASIC,
                                            &handle_info, sizeof(handle_info), NULL, NULL);
    if (status != ZX_OK) {
        return status;
    }

    if (!have_local_clone_ && !WindowMatchesVMO(vmo_, offset_, length_)) {
        status = MakeLocalClone(handle_info.rights & ZX_RIGHT_EXECUTE);
        if (status != ZX_OK) {
            return status;
        }
    }

    // Drop write rights.
    zx_handle_t vmo;
    status = zx_handle_duplicate(
        vmo_,
        ZX_RIGHT_READ | ZX_RIGHT_MAP |
        ZX_RIGHTS_BASIC | ZX_RIGHT_GET_PROPERTY |
        (handle_info.rights & ZX_RIGHT_EXECUTE), // Preserve exec if present.
        &vmo);
    if (status != ZX_OK) {
        return status;
    }

    info->tag = fuchsia_io_NodeInfoTag_vmofile;
    info->vmofile.vmo = vmo;
    info->vmofile.offset = offset_;
    info->vmofile.length = length_;
    return ZX_OK;
}

zx_status_t VnodeVmo::Read(void* data, size_t len, size_t off, size_t* out_actual) {
    if (off > length_) {
        *out_actual = 0;
        return ZX_OK;
    }
    size_t rlen = length_ - off;
    if (len > rlen) {
        len = rlen;
    }
    zx_status_t status = zx_vmo_read(vmo_, data, offset_ + off, len);
    if (status == ZX_OK) {
        *out_actual = len;
    }
    return status;
}

zx_status_t VnodeVmo::Getattr(vnattr_t* attr) {
    memset(attr, 0, sizeof(vnattr_t));
    attr->inode = ino_;
    attr->mode = V_TYPE_FILE | V_IRUSR;
    attr->size = length_;
    attr->blksize = kMemfsBlksize;
    attr->blkcount = fbl::round_up(attr->size, kMemfsBlksize) / VNATTR_BLKSIZE;
    attr->nlink = link_count_;
    attr->create_time = create_time_;
    attr->modify_time = modify_time_;
    return ZX_OK;
}

zx_status_t VnodeVmo::GetVmo(int flags, zx_handle_t* out_vmo, size_t* out_size) {
    if (!have_local_clone_ && !WindowMatchesVMO(vmo_, offset_, length_)) {
        zx_info_handle_basic_t handle_info;
        zx_status_t status = zx_object_get_info(vmo_, ZX_INFO_HANDLE_BASIC,
                                                &handle_info, sizeof(handle_info), NULL, NULL);
        if (status != ZX_OK) {
            return status;
        }
        status = MakeLocalClone(handle_info.rights & ZX_RIGHT_EXECUTE);
        if (status != ZX_OK) {
            return status;
        }
    }
    if (flags & fuchsia_io_VMO_FLAG_WRITE) {
        return ZX_ERR_NOT_SUPPORTED;
    }

    // Let clients map and set the names of their VMOs.
    zx_rights_t rights = ZX_RIGHTS_BASIC | ZX_RIGHT_MAP | ZX_RIGHTS_PROPERTY;
    // We can ignore fuchsia_io_VMO_FLAG_PRIVATE, since private / shared access
    // to the underlying VMO can both be satisfied due to the immutability of
    // Vmofiles.
    rights |= (flags & fuchsia_io_VMO_FLAG_READ) ? ZX_RIGHT_READ : 0;
    rights |= (flags & fuchsia_io_VMO_FLAG_EXEC) ? ZX_RIGHT_EXECUTE : 0;

    zx_handle_t vmo;
    zx_status_t status = zx_handle_duplicate(vmo_, rights, &vmo);
    if (status != ZX_OK) {
        return status;
    }

    *out_vmo = vmo;
    *out_size = length_;
    return ZX_OK;
}

zx_status_t VnodeVmo::MakeLocalClone(bool executable) {
    zx_handle_t tmp_vmo;
    zx_status_t status = zx_vmo_create_child(vmo_, ZX_VMO_CHILD_COPY_ON_WRITE,
                                             offset_, length_, &tmp_vmo);
    if (status != ZX_OK) {
        return status;
    }

    // Restore ZX_RIGHT_EXECUTE, if necessary.
    // TODO(mdempsky): Use non-COW clone once available.
    if (executable) {
        status = zx_vmo_replace_as_executable(tmp_vmo, ZX_HANDLE_INVALID, &vmo_);
        if (status != ZX_OK) {
            return status;
        }
    } else {
        vmo_ = tmp_vmo;
    }

    offset_ = 0;
    have_local_clone_ = true;
    return ZX_OK;
}

} // namespace memfs