10th. Synchronizing device I/O and asynchronous device I/O (1)

10.1 turning the device on and off

10.1.1 The definition of a device -anything that can be communicated with in Windows.

(1) common equipment and uses

Equipment	Use	function to open the device
File	Permanently store any data	CreateFile (Pszname is a pathname or a UNC path name)
Directory	Settings for properties and file compression	Ditto, if you specify the FILE_FLAG_BACKUP_SEMANTICS flag, a directory opens. You can change the properties of a directory (such as normal or hidden) and their timestamps
Logical Disk Drives	Format Drive	CreateFile (Pszname is \\.\x:) where x is the drive letter. can be used to format the drive or detect the size of the drive medium
Physical Disk Drives	accessing partitioned Tables	CreateFile (Pszname is \\.\physicaldrivex:) opens the physical drive, whose x is the letter of the physical drive. such as \\.\PHYSICALDRIVE0, represents the first physical drive
Serial	Transmitting data over a telephone line	CreateFile (Pszname for "COMx")
and the port	Transferring data to the printer	CreateFile (Pszname for "LPTx")
Mail slots	One-to-many data transfer, usually via a network to another running Windows machine	Mail slot server: Createmailslot (pszname for "\\.\mailslot\mailslotname") Mail Slot client: Createmailslot (pszname as "\\servername\mailslot\mailslotname")
Named pipes	Single-to-one data transfer, usually via a network to another machine running Windows	Server side: Createnamepipe (Pszname for "\\.\pipe\pipename") Client: CreateFile (Pszname for "\\servername\pipe\pipename")
Anonymous pipeline	One-to-one data transfer on a single machine (never Across networks)	CreatePipe used to open servers and clients
Sockets	Transmission of a message or data stream, usually via a network to any machine that supports the use of a word (the machine does not necessarily run the Windows operating system	Socket, accept, or AcceptEx
Control Desk	Screen caching in the text window	Createconsolescreenbuffer or GetStdHandle

(2) Set the parameters for communication with the device, such as Setcommconfig set the baud rate of the serial port; setmailslotinfo sets the timeout value for the time-out message slot.

(3) Turn off communication: For most devices, call CloseHandle, but socket with closesocket

(4) Get the device type: Getfiletype, the return value is as follows

①file_type_unknown: Unknown type ②file_type_disk: Disk File

③file_type_char: Character file, commonly referred to as a common port and device or console

④file_type_pipe: Named pipes or anonymous pipelines

10.1.2 Look at CreateFile

(1) CreateFile function

Parameters	Describe
Pszname	Can be either a device type or an instance of a device of that class
dwDesiredAccess	How to transfer data 0: Can only change the configuration of the device, can not read data or write data Generic_read: Allow read-only access to the device Generic_write: Write-only access (note not readable) generic_read| Generic_write: Readable and writable
dwShareMode	Specify shared privileges for Devices ①0: Exclusive access to devices . The CreateFile call fails if the device is already open. Similarly, if we successfully open the device, then the subsequent CreateFile will fail. ②file_share_read: Shared Read Only (cannot modify device data) A, Our CreateFile will fail if the device has been opened in write-only or exclusive mode. B, if we open successfully, subsequent calls to CreateFile using Generic_write will fail. ②file_share_write: share only write (cannot read device data) A, Our CreateFile will fail if the device has been opened in read-only or exclusive mode. B, if we open successfully, subsequent calls to CreateFile using Generic_read will fail. ③file_share_write| File_share_read: Shared read/write A, our CreateFile will fail if the device is already open exclusively. B, if we open successfully, then the subsequent requirements Exclusive Read ( is dwsharemode=0, Span style= "color: #ff0000;" >dwdesiredaccess=generic_read), exclusive write , or exclusive read/write call CreateFile will fail. ④file_share_delete: When you delete or move a file, it is flagged for deletion and is actually deleted when all open handles are closed.
Psa	The security attribute, usually set to NULL, Returns a handle that is not inheritable by default.
Dwcreatedisposition	The meaning of the file is greater than the type of other devices Create_new: Create a new file, CreateFile fails if there is a file with the same name Create_always: Creates a new file, overwriting the old file, regardless of whether it has the same name open_existing: Open the file or device that you own, and if it does not, CreateFile fails. If you are opening a device other than a file, you must set the flag. Open_always: If the file already exists, open it directly. If it does not exist, it is created and then opened. Truncate_exisiting: Open your own file and truncate the file size to 0
dwFlagsAndAttributes	Used to fine-tune communication with the device (if it is a file, set the properties of the file)( see 2nd later analysis )
Hfiletemplate	can be null, or it can be a file handle ① If Hfiletemplate identifies a file handle, the dwFlagsAndAttributes parameter is ignored and the Hfiletemplate template file's properties are used instead, but hfiletemplate must first be generic_ Read Open. ② hfiletemplate is ignored if CreateFile is to be opened instead of creating a new file
return value	Success: Return file or device handle Failure: Invalid_handle_value (-1), note not null!

10th. Synchronizing device I/O and asynchronous device I/O (1)