zircon/system/ulib/memfs/file.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 {

// Artificially cap the maximum in-memory file size to 512MB.
constexpr size_t kMemfsMaxFileSize = 512 * 1024 * 1024;

VnodeFile::VnodeFile(Vfs* vfs)
    : VnodeMemfs(vfs), vmo_size_(0), length_(0)  {}

VnodeFile::~VnodeFile() {
    vfs()->WillFreeVMO(vmo_size_);
}

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

zx_status_t VnodeFile::Read(void* data, size_t len, size_t off, size_t* out_actual) {
    if ((off >= length_) || (!vmo_.is_valid())) {
        *out_actual = 0;
        return ZX_OK;
    } else if (len > length_ - off) {
        len = length_ - off;
    }

    zx_status_t status = vmo_.read(data, off, len);
    if (status == ZX_OK) {
        *out_actual = len;
    }
    return status;
}

zx_status_t VnodeFile::Write(const void* data, size_t len, size_t offset,
                             size_t* out_actual) {
    zx_status_t status;
    if (offset > kMemfsMaxFileSize) {
        return ZX_ERR_FILE_BIG;
    }
    size_t newlen;
    if (add_overflow(offset, len, &newlen)) {
        return ZX_ERR_FILE_BIG;
    }
    newlen = newlen > kMemfsMaxFileSize ? kMemfsMaxFileSize : newlen;
    if ((status = vfs()->GrowVMO(vmo_, vmo_size_, newlen, &vmo_size_)) != ZX_OK) {
        return status;
    }
    // Accessing beyond the end of the file? Extend it.
    if (offset > length_) {
        // Zero-extending the tail of the file by writing to
        // an offset beyond the end of the file.
        ZeroTail(length_, offset);
    }
    size_t writelen = newlen - offset;
    if ((status = vmo_.write(data, offset, writelen)) != ZX_OK) {
        return status;
    }
    *out_actual = writelen;

    if (newlen > length_) {
        length_ = newlen;
    }
    if (writelen < len) {
        // short write because we're beyond the end of the permissible length
        return ZX_ERR_FILE_BIG;
    }
    UpdateModified();
    return ZX_OK;
}

zx_status_t VnodeFile::Append(const void* data, size_t len, size_t* out_end,
                              size_t* out_actual) {
    zx_status_t status = Write(data, len, length_, out_actual);
    *out_end = length_;
    return status;
}

zx_status_t VnodeFile::GetVmo(int flags, zx_handle_t* out_vmo, size_t* out_size) {
    zx_status_t status;
    if (!vmo_.is_valid()) {
        // First access to the file? Allocate it.
        if ((status = zx::vmo::create(0, ZX_VMO_RESIZABLE, &vmo_)) != ZX_OK) {
            return status;
        }
    }

    // Let clients map and set the names of their VMOs.
    zx_rights_t rights = ZX_RIGHTS_BASIC | ZX_RIGHT_MAP | ZX_RIGHTS_PROPERTY;
    rights |= (flags & fuchsia_io_VMO_FLAG_READ) ? ZX_RIGHT_READ : 0;
    rights |= (flags & fuchsia_io_VMO_FLAG_WRITE) ? ZX_RIGHT_WRITE : 0;
    rights |= (flags & fuchsia_io_VMO_FLAG_EXEC) ? ZX_RIGHT_EXECUTE : 0;
    zx::vmo result;
    if (flags & fuchsia_io_VMO_FLAG_PRIVATE) {
        if ((status = vmo_.create_child(ZX_VMO_CHILD_COPY_ON_WRITE, 0, length_,
                                        &result)) != ZX_OK) {
            return status;
        }

        if ((status = result.replace(rights, &result)) != ZX_OK) {
            return status;
        }
        *out_vmo = result.release();
        *out_size = length_;
        return ZX_OK;
    }

    if ((status = vmo_.duplicate(rights, &result)) != ZX_OK) {
        return status;
    }
    *out_vmo = result.release();
    *out_size = length_;
    return ZX_OK;
}

zx_status_t VnodeFile::Getattr(vnattr_t* attr) {
    memset(attr, 0, sizeof(vnattr_t));
    attr->inode = ino_;
    attr->mode = V_TYPE_FILE | V_IRUSR | V_IWUSR | V_IRGRP | V_IROTH;
    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 VnodeFile::GetNodeInfo(uint32_t flags, fuchsia_io_NodeInfo* info) {
    info->tag = fuchsia_io_NodeInfoTag_file;
    return ZX_OK;
}

zx_status_t VnodeFile::Truncate(size_t len) {
    zx_status_t status;
    if (len > kMemfsMaxFileSize) {
        return ZX_ERR_INVALID_ARGS;
    }
    if ((status = vfs()->GrowVMO(vmo_, vmo_size_, len, &vmo_size_)) != ZX_OK) {
        return status;
    }
    if (len < length_) {
        // Shrink the logical file length.
        // Zeroing the tail here is optional, but it saves memory.
        ZeroTail(len, length_);
    } else if (len > length_) {
        // Extend the logical file length.
        ZeroTail(length_, len);
    }

    length_ = len;
    UpdateModified();
    return ZX_OK;
}

void VnodeFile::ZeroTail(size_t start, size_t end) {
    constexpr size_t kPageSize = static_cast<size_t>(PAGE_SIZE);
    if (start % kPageSize != 0) {
        char buf[kPageSize];
        size_t ppage_size = kPageSize - (start % kPageSize);
        memset(buf, 0, ppage_size);
        ZX_ASSERT(vmo_.write(buf, start, ppage_size) == ZX_OK);
    }
    end = fbl::min(fbl::round_up(end, kPageSize), vmo_size_);
    uint64_t decommit_offset = fbl::round_up(start, kPageSize);
    uint64_t decommit_length = end - decommit_offset;

    if (decommit_length > 0) {
        ZX_ASSERT(vmo_.op_range(ZX_VMO_OP_DECOMMIT, decommit_offset,
                                decommit_length, nullptr, 0) == ZX_OK);
    }
}

} // namespace memfs