December 2013
Intermediate to advanced
496 pages
8h 57m
Chinese
Content preview from LINUX系統程式設計 第二版
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第八章
裝置節點
裝置節點
（
device node
）是一種特殊檔案，應用程式可以透過它介接裝置驅動程式
（device driver）。當應用程式在一個裝置節點上進行平常的 Unix I/O 時—像是開啟、
關閉、讀取、寫入…等等，核心並不會像一般檔案 I/O 那樣來處理這些要求。事實上，
核心會將此類要求傳遞給一個裝置驅動程式。裝置驅動程式會處理該 I/O 操作，以及把
結果傳回給用戶。裝置節點所提供的裝置抽象層，讓應用程式不需要熟悉裝置的具體情
況，甚至不必掌控特殊的介面。的確，在 Unix 系統上，裝置節點是存取硬體的標準機
制。網路裝置是罕見的例外，並且在 Unix 的歷史中，對此例外是否為錯誤有些爭論。
使用
read()
、
write()
及
mmap()
等呼叫來操作一個機器的所有硬體，的確具有一種優雅
的美感。
核心如何辨別應該由哪個裝置驅動程式來處理要求？每個裝置節點會被指定兩個數值，
稱為
主要編號
（
major numbe
r）及
次要編號
（
minor number
）。這些主要和次要編號會映
射至被載入核心的特定裝置驅動程式。如果一個裝置節點所具有的主要和次要編號並未
映射至核心裡的裝置驅動程式—會因為各種原因突然發生此情況—則裝置節點上的一個
open()
要求，會傳回
-1
並且把
errno
設定為
ENODEV
。於是我們會說，此裝置節點碰上了
不存在的裝置。
特殊裝置節點
特殊裝置節點存在於所有的 Linux 系統之上。這些裝置節點是 Linux 開發環境的一部
分，而且它們的存在被視為 Linux ABI ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.