探寻Linux FTL通用设备层的应用与优势 (linux ftl 通用设备层)

随着信息技术的不断发展，数据存储与处理已经成为了企业发展过程中重要的一环。而作为存储技术的基础之一，存储介质的发展越来越由硬件向软件方向发展。在这个背景下，Linux FTL通用设备层（FTL，Flash Translation Layer）的应用与优势越来越被人们关注。

一、Linux FTL通用设备层的概念与发展

在之前的存储介质中，例如磁盘，它们使用的是磁盘调度算法，通过分为循环队列等方式进行数据的管理。而在存储介质逐渐由磁盘向Flash发展过程中，由于Flash芯片的读写速度很快，因此采用了FTL技术。

FTL技术的产生主要是基于Flash芯片的特性，他本身是不支持随意改变已经存储的数据，也就是常说的“只能写不能改”，因此必须要有一种将新数据转化成Flash芯片可识别的方式，而FTL便是实现这一过程的一种技术手段。

而随着Linux操作系统的不断成长，章文嵩先生在加拿大滑铁卢大学于2023年发表“通用Linux Flash Translation Layer”，它是一种硬件抽象层，为文件系统层提供与Flash存储介质的通信，并进行数据块的管理和映射。

二、Linux FTL通用设备层的应用

FTL技术已经广泛应用于各种Flash存储介质中，例如USB存储设备、固态硬盘、以及现在越来越流行的移动设备等，而Linux FTL通用设备层的应用范围也不断扩大。

1.移动设备

在移动设备中，Linux FTL通用设备层技术不断优化将Flash储存技术用在移动设备中，其可靠性和性能都得到了很好的提升。尤其是在安卓操作系统中，Linux FTL通用设备层技术已经得到广泛应用，并为人们带来了更加先进的移动设备体验。

2.车载娱乐系统

Linux FTL通用设备层技术也被广泛应用于车载娱乐系统中。在这个系统中，大量的集成电路、嵌入式Linux操作系统和人机交互技术被运用，以实现音频、视频、导航等功能。

3.工业控制

在工业控制领域，Linux FTL通用设备层技术也被广泛应用。在控制过程中，工控机的存储器对于特定控制器内的代码和数据至关重要，而Linux FTL通用设备层技术可有效保证这些数据的读写效率和稳定性。

三、Linux FTL通用设备层的优势

Linux FTL通用设备层技术具有以下优势：

1.良好的可扩展性

Linux FTL通用设备层技术通过模块化的设计思路，允许用户根据自身需要自由拓展功能。用户可以将支持不同的Flash芯片的模块添加到系统中，从而实现通用性。

2.良好的稳定性

FTL技术的主要作用是在文件系统和硬盘之间进行数据翻译，保证数据正常传输且不被破坏，因此稳定性是必须的。而FTL技术在保证其高性能的情况下，其稳定性也得到了良好保障。

3.良好的兼容性

FTL技术与现有的操作系统兼容性非常良好，无需专门针对某一种操作系统的设计，可以广泛使用于各种系统中。

四、

总体而言，随着信息的不断更新，感知持续变化下的技术发展需求，Linux FTL通用设备层将会在存储介质的发展中发挥更大的作用。Linux FTL通用设备层技术已经被大量应用于移动设备、车载娱乐系统、工业控制等领域，具有良好的可扩展性，稳定性和兼容性。未来，Linux FTL通用设备层还将不断发展，为存储技术的创新打下坚实的基础。

相关问题拓展阅读：

• LINUX 终端设备驱动？
• 求有关linux的英文资料！！谢谢
• LINUX系统的特点是什么

LINUX 终端设备驱动？

在Linux系统中，终端是一种字符型设备，它有多种类型，通常使用tty (Teletype）来简称各种类型的终端设备。对于嵌入式系统而言，最普遍采用的是UART (Universal Asynchronous Receiver/Tranitter)串行端口，日常生活中简称串口。

Linux内核中tty的层次结构它包含tty核心tty_10.c、tty或路规在n_tty.C(头现N_11Y线路规程）和tty驱动实例xxx_tty.c，激慧tty线路规程的工作是以特殊的方式格式化从一个用户或者硬件收到的数据，这种格式化常常采用一个协议转换的形式tty _io.c本身是一个标准的字符设备驱动，它对上有字符改备的职贡，买现tle_operatIonS双贝图效。但是tty核心层对下又定义了tty_driver的架构，这样tty设备驱动的主体工作就变成了琪允tty_driVeT依构体中的成员，实现其中的tty_operations的成员函数，而不再是去实现file_operations这一级的工作。tty设枯衡备发送数据的流程为:tty核心从一个用户获取将要发送给一个tty设备的数据，tty核心将数据传递给tty线路规程驱动，接着数据被传递到tty驱动，tty驱动将数据转换为可以发送给硬件的格式。接收数据的流程为:从tty硬件接收到的数据向上交给tty驱动，接着进入tty线路规程驱动，再进入tty核心，在这里它被一个用户获取。尽管一个特定的底层UART设备驱动完全可以遵循上述tty_driver的方法来设计，即定义tty_driver并实现tty_operations中的成员函数，但是鉴于串口之间的共性，Linux考虑在文件drivers’ttyliserial’serial_core.c中实现了UART设备的通用tty驱动层（我们可以称其为串口核心层)。这样，UART驱动的明败答主要任务就进一步演变成了实现serial-core.c中定义的一组uart_xxx接口而不是tty_xxx接口。因此，按照面向对象的思想，可以认为tty_driver是字符设备的泛化、serial-core是tty_driver的泛化，而具体的串口驱动又是serial-core的泛化。

求有关linux的英文资料！！谢谢

wiki网站，看linux词条。。。

Anatomy of Linux flash file systems

Options and architectures

Summary: You’ve probably heard of Journaling Flash File System (JFFS) and Yet

Another Flash File System (YAFFS), but do you know what it means to have a file

system that assumes an underlying flash device? This article introduces you to

flash file systems for Linux®, explores how they care for their underlying

consumable devices (flash parts) through wear leveling, and identifies the

various flash file systems available along with their fundamental designs.

Solid-state drives are all the rage these days, but embedded systems have

used solid-state devices for storage for quite some time. You’ll find flash

file systems used in personal digital assistants (PDAs), cell phones, MP3

players, digital cameras, USB flash drives (UFDs), and even laptop computers.

In many cases, the file systems for commercial devices can be custom and

proprietary, but they face the same challenges discussed below.

Flash-based file systems come in a variety of forms. This article explores

a couple of the read-only file systems and also reviews the various read/write

file systems available today and how they work. But first, let’s explore the

flash devices and the challenges that they introduce.

Flash memory technologies

Flash memory, which can come in several different technologies, is non-volatile

memory, which means that its contents persist after its source of power is

removed. For a great history of flash memory devices, see Resources.

Two of the most common types of flash devices are defined by their

respective technologies: NOR and NAND. NOR-based flash is the older technology

that supported high read performance at the expense of aller capacities. NAND

flash offers higher capacities with significantly faster write and erase

performance. NAND also requires a much more complicated input/output (I/O)

interface.

Flash parts are commonly divided into partitions, which allows

multiple operations to occur simultaneously (erasing one partition while

reading from another). Partitions are further divided into blocks

(commonly 64KB or 128KB in size). Firmware that uses the partitions can further

apply unique segmenting to the blocks—for example, 512-byte segments within a

block, not including metadata.

Flash devices exhibit a common constraint that requires device management

when compared to other storage devices such as RAM disks. The only Write

operation permitted on a flash memory device is to change a bit from a one to a

zero. If the reverse operation is needed, then the block must be erased (to

reset all bits to the one state). This means that other valid data within the

block must be moved for it to persist. NOR flash memory can typically be

programmed a byte at a time, whereas NAND flash memory must be programmed in

multi-byte bursts (typically, 512 bytes).

The process of erasing a block differs between the two memory types. Each

requires a special Erase operation that covers an entire block of the flash

memory. NOR technology requires a precursor step to clear all values to zero

before the Erase operation can begin. An Erase is a special operation

with the flash device and can be time-consuming. Erasing is an electrical

operation that drains the electrons from each cell in an entire block.

NOR flash devices typically require seconds for the Erase operation,

whereas a NAND device can erase in milliseconds. A key characteristic of flash

devices is the number of Erase operations that can be performed. In a NOR

device, each block in the flash memory can be erased up to 100,000 times. NAND

flash memories can be erased up to one million times.

Flash memory challenges

In addition to and as a result of the constraints explored in the previous

section, managing flash devices presents several challenges. The three most

important are garbage collection, managing bad blocks, and wear leveling.

Garbage collection

Garbage collection is the process of reclaiming invalid blocks (those that

contain some amount of invalid data). Reclamation involves moving the valid

data to a new block, and then erasing the invalid block to make it available.

This process is commonly done in the background or as needed, if the file

system is low on available space.

Managing bad blocks

Over time, flash devices can develop bad blocks through use and can even

ship from the manufacturer with blocks that are bad and cannot be used. You can

detect the presence of back blocks from a failed flash operation (such as an

Erase) or an invalid Write operation (discovered through an invalid Error

Correction Code, or ECC).

After bad blocks have been identified, they are marked within the flash

itself in a bad block table. How this is done is device-dependent but can be

implemented with a separate set of reserved blocks managed separately from

normal data blocks. The process of handling bad blocks—whether they ship with

the device or appear over time—is called bad block management. In some

cases, this functionality is implemented in hardware by an internal

microcontroller and is therefore transparent to the upper-level file system.

Wear leveling

Recall that flash devices are consumable parts: You can perform a finite

number of Erase cycles on each block before the block becomes bad (and must

therefore be tagged by bad block management). To maximize the life of the

flash, wear-leveling algorithms are provided. Wear leveling comes in two

varieties: dynamic wear leveling and static wear leveling.

Dynamic wear leveling addresses the problem of a limited number of Erase

cycles for a given block. Rather than randomly using blocks as they are

available, dynamic wear-leveling algorithms attempt to evenly distribute the

use of blocks so that each gets uniform use. Static wear-leveling algorithms

address an even more interesting problem. In addition to a maximum number of

Erase cycles, certain flash devices suffer from a maximum number of Read cycles

between Erase cycles. This means that if data sits for too long in a block and

is read too many times, the data can dissipate and result in data loss. Static

wear-leveling algorithms address this by periodically moving stale data to new

blocks.

System architecture

So far, I’ve explored flash devices and their fundamental challenges. Now,

look at how these pieces come together as part of a layered architecture (see

Figure 1). At the top is the virtual file system (VFS), which presents a common

interface to higher-level applications. The VFS is followed by the flash file

system, which will be covered in the next section. Next is the Flash

Translation Layer (FTL), which provides for overall management of the flash

device, including allocation of blocks from the underlying flash device as well

as address translation, dynamic wear leveling, and garbage collection. In some

flash devices, a portion of the FTL can be implemented in hardware.

The Linux kernel uses the Memory Technology Device (MTD) interface, which

is a generic interface for flash devices. The MTD can automatically detect the

width of the flash device bus and the number of devices necessary for

implementing the bus width.

Flash file systems

Several flash file systems are available for Linux. The next sectionsexplain the design and advantages of each.

Journaling Flash File System

One of the earliest flash file systems for Linux is called the Journaling

Flash File System. JFFS is a log-structured file system that was designed

for NOR flash devices. It was unique and addressed a variety of problems with

flash devices, but it created another.

JFFS viewed the flash device as a circular log of blocks. Data written to

the flash is written to the tail, and blocks at the head are reclaimed. The

space between the tail and head is free space; when this space becomes low, the

garbage collector is executed. The garbage collector moves valid blocks to the

tail of the log, skips invalid or obsolete blocks, and erases them (see Figure

2). The result is a file system that is automatically wear leveled both

statically and dynamically. The fundamental problem with this architecture is

that the flash device is erased too often (instead of an optimal erase

strategy), which wears the device out too quickly.

When a JFFS is mounted, the structural details are read into memory, whichcan be slow at mount-time and consume more memory than desired.

Journaling Flash File System 2

Although JFFS was very useful in its time, its wear-leveling algorithm

tended to shorten the life of NOR flash devices. The result was a redesign of

the underlying algorithm to remove the circular log. The JFFS2 algorithm was

designed for NAND flash devices and also includes improved performance with

compression.

In JFFS2, each block in the flash is treated independently. JFFS2 maintains

block lists to sufficiently wear-level the device. The clean list represents

blocks on the device that are full of valid nodes. The dirty list contains

blocks with at least one obsoleted node. Finally, the free list represents the

blocks that have been erased and are available for use.

The garbage collection algorithm can then intelligently decide what to

reclaim in a reasonable way. Currently, the algorithm probabilistically selects

from the clean or dirty list. The dirty list is selected 99 percent of the time

to reclaim blocks (moving the valid contents to another block), and the clean

list is selected 1 percent of the time (simply moving the contents to a new

block). In both cases, the selected block is erased and placed on the free list

(see Figure 3). This allows the garbage collector to re-use blocks that are

obsoleted (or partially so) but still move data around the flash to support

static wear leveling.

Yet Another Flash File System

YAFFS is another flash file system developed for NAND flash. The initial

version (YAFFS) supported flash devices with 512-byte pages, but the newer

version (YAFFS2) supports newer devices with larger page sizes and greater

Write constraints.

In most flash file systems, obsolete blocks are marked as such, but YAFFS2

additionally marks blocks with monotonically increasing sequence numbers. When

the file system is scanned at mount time, the valid inodes can be quickly

identified. YAFFS also maintains trees in RAM to represent the block structure

of the flash device, including fast mounting through checkpointing —the

process of saving the RAM tree structure to the flash device on a normal

unmount so that it can be quickly read and restored to RAM at mount time (see

Figure 4). Mount-time performance is a great advantage of YAFFS2 over other

flash file systems.

Read-only compressed file systems

In some embedded systems, there’s no need to provide a mutable file system:

An immutable one will suffice. Linux supports a variety of read-only file

systems, two of the most useful are cramfs and SquashFS.

Cramfs

The cramfs file system is a compressed read-only Linux file system that can

exist within flash devices. The primary characteristics of cramfs are that it

is both simple and space-efficient. This file system is used in all-footprint

embedded designs.

While cramfs metadata is not compressed, cramfs uses zlib compression on a

per-page basis to allow random page access (pages are decompressed upon

access).

You can play with cramfs using the mkcramfs utility and the loopbackdevice.

SquashFS

SquashFS is another compressed read-only Linux file system that is useful

within flash devices. You’ll also find SquashFS in numerous Live CD Linux

distributions. In addition to supporting zlib for compression, SquashFS uses

Lembel-Ziv-Markov chain Algorithm (LZMA) for improved compression and speed.

Like cramfs, you can use SquashFS on a standard Linux system withmksquashfs and the loopback device.

Going further

Like most of open source, software continues to evolve, and new flash file

systems are under development. An interesting alternative still in development

is LogFS, which includes some very novel ideas. For example, LogFS maintains a

tree structure on the flash device itself so that the mount times are similar

to traditional file systems, such as ext2. It also uses a wandering tree for

garbage collection (a form of B+tree). What makes LogFS particularly

interesting, however, is that it is very scalable and can support large flash

parts.

With the growing popularity of flash file systems, you’ll see a

considerable amount of research being applied toward them. LogFS is one

example, but other options, such as UbiFS, are also growing. Flash file systems

are interesting architecturally and will continue to be a source of innovationin the future.

google之，

最简单的是 google学术里面输入 linux 搜索你要的文献

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LINUX系统的特点是什么

Linux（i/?l?n?ks/LIN-?ks）是一种自由和开放源码的类UNIX操作系统。该操作系统的内核由林纳斯·托瓦兹在1991年10月5日首次渣段高发布，在加上用户空间的应用程序之后，成为Linux操作系统。

Linux也是自由软件和开放源代码软件发展中最著名的例子。只要遵循GNU通用公共许可证（GPL），任何个人和机构都可以自由地使燃慧用Linux的所有底层源代码，也可以自由地修改和再发布。大多数Linux系统还包括像提供GUI的XWindow之类的程序。

LINUX系统的特点

1、Linux是一款免费的操作系统，用户可以通过网络或其他途径免费获得，并可以任意修改其源代码。这是其他的操作系统所做不到的。

2、在Linux下通过相应的模拟器运行常见的DOS、Windows的程序。这为用户从Windows转到Linux奠定了基础。

3、Linux可以运行在多种硬件平台上，如具有x86、680×0、SPARC、Alpha等处如尺理器的平台。此外Linux还是一种嵌入式操作系统，可以运行在掌上电脑、机顶盒或游戏机上。

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