DosOpen2

This call opens a new file, an existing file, or a replacement for an existing file. The opened file can have extended attributes.

DosOpen2

(FileName, FileHandle, ActionTaken, FileSize, FileAttribute, OpenFlag, OpenMode, EABuf, Reserved)

FileName (PSZ) - input

Address of the ASCIIZ path name of the file to be opened.
FileHandle (PHFILE) - output
Address of the handle for the file.
ActionTaken (PUSHORT) - output
Address of the action taken as a result of DosOpen2.

Value

Definition
0001H
File exists
0002H
File created
0003H
File replaced.
FileSize (ULONG) - input
File's new logical size (EOD), in bytes. This parameter is significant only when creating a new file or replacing an existing file. Otherwise, it is ignored.
FileAttribute (USHORT) - input
File attribute bits. Defined below:

Bit

Description
15-6
Reserved and must be zero.
5
File archive
4
Subdirectory
3
Reserved and must be zero.
2
System file
1
Hidden file
0
Read only file
These bits may be set individually or in combination. For example, an attribute value of 0021H (bits 5 and 0 set to 1) indicates a read-only file that should be archived.
OpenFlag (USHORT) - input
One-word field indicates the action to be taken if the file exists or does not exist.

Bit

Description
15-8
Reserved and must be zero.
7-4
0000 = Fail if file does not exist.

0001 = Create file if file does not exist.

3-0
0000 = Fail if the file already exists.

0001 = Open the file if it already exists.

0010 = Replace the file if it already exists.

OpenMode (ULONG) - input
The OpenMode parameter contains the following bit flags:

Bit

Description
15
DASD Open flag:

0 = FileName represents a file to be opened in the normal way.

1 = FileName is "Drive:" and represents a mounted disk or diskette volume to be opened for direct access.

14
Write-Through flag:

0 = Writes to the file may be run through the file system buffer cache.

1 = Writes to the file may go through the file system buffer cache but the sectors are written (actual file I/O completed) before a synchronous write call returns. This state of the file defines it as a synchronous file. For synchronous files, this is a mandatory bit in that the data must be written out to the medium for synchronous write operations.

This bit is not inherited by child processes.

13
Fail-Errors flag. Media I/O errors are handled as follows:

0 = Reported through the system critical error handler.

1 = Reported directly to the caller by way of return code.

Media I/O errors generated through an IOCTL Category 8 function always get reported directly to the caller by way of return code. The Fail-Errors function applies only to non-IOCTL handle-based file I/O calls.

This bit is not inherited by child processes.

12
No-Cache/Cache flag:

0 = It is advisable for the disk driver to cache the data in I/O operations on this file.

1 = I/O to the file need not be done through the disk driver cache.

This bit advises FSDs and device drivers whether it is worth caching the data. Like the write-through bit, this is a per-handle bit and is not inherited by child processes.

11
Reserved and must be zero.
10-8
The locality of reference flags contain information about how the application is to access the file.
Value
Definition
000
No locality known.
001
Mainly sequential access.
010
Mainly random access.
011
Random with some locality.
7
Inheritance flag:

0 = File handle is inherited by a spawned process resulting from a DosExecPgm call.

1 = File handle is private to the current process.

This bit is not inherited by child processes.

6-4
Sharing Mode flags. This field defines any restrictions to file access placed by the caller on other processes:
Value
Definition
001
Deny Read/Write access
010
Deny Write access
011
Deny Read access
100
Deny neither Read or Write access (Deny None). Any other value is invalid.
3
Reserved and must be zero.
2-0
Access Mode flags. This field defines file access required by the caller:
Value
Definition
000
Read-Only access
001
Write-Only access
010
Read/Write access. Any other value is invalid.
Any other combinations are invalid.
File sharing requires the cooperation of sharing processes. This cooperation is communicated through sharing and access modes. Any sharing restrictions placed on a file opened by a process are removed when the process closes the file with a DosClose request.

Sharing Mode

Specify the type of access other processes may have to the file (sharing mode). For example, if it is permissible for other processes to continue reading the file while your process is operating on it, specify Deny Write. This sharing mode prevents other processes from writing to the file but still allows them to read it.
Access Mode
Specify the type of access to the file needed by your process (access mode).
For example, if your process requires Read/Write access, and another process has already opened the file with a sharing mode of Deny None, your DosOpen2 request succeeds. However, if the file is open with a sharing mode of Deny Write, your process is denied access.
If the file is inherited by a child process, all sharing and access restrictions are also inherited.
If an open file handle is duplicated by a call to DosDupHandle, all sharing and access restrictions are also duplicated.
EABuf (PEAOP) - input/output
Address of the extended attribute buffer, which contains an EAOP structure. An EAOP structure has the following format:

fpGEAList (PGEALIST)

Address of GEAList. GEAList is a packed array of variable length "get EA" structures, each containing an EA name and the length of the name.
fpFEAList (PFEALIST)
Address of FEAList. FEAList is a packed array of variable length "full EA" structures, each containing an EA name and its corresponding value, as well as the lengths of the name and the value.
oError (ULONG)
Offset into structure where error has occurred.
On input, the fpGEAList field and oError fields are ignored. The EA setting operation is performed on the information contained in FEAList. If extended attributes are not to be defined or modified, then EABuf must be set to null. Following is the FEAList format:

cbList (ULONG)

Length of the FEA list, including the length itself.
list (FEA)
List of FEA structures. An FEA structure has the following format:

Flags (BYTE)

Bit indicator describing the characteristics of the EA being defined.

Bit

Description
7
Critical EA.
6-0
Reserved and must be set to zero.

If bit 7 is set to 1, this indicates a critical EA. If bit 7 is 0, this means the EA is noncritical; that is, the EA is not essential to the intended use by an application of the file with which it is associated.

cbName (BYTE)
Length of EA ASCIIZ name, which does not include the null character.
cbValue (USHORT)
Length of EA value, which cannot exceed 64KB.
szName (PSZ)
Address of the ASCIIZ name of EA.
aValue (PSZ)
Address of the free-format value of EA.
Note:
The szName and aValue fields are not included as part of header or include files. Because of their variable lengths, these entries must be built manually.
On output, fpGEAList is unchanged. fpFEAList is unchanged as is the area pointed to by fpFEAList. If an error occurred during the set, oError is the offset of the FEA where the error occurred. The API return code is the error code corresponding to the condition generating the error. If no error occurred, oError is undefined.

If EABuf is 0x00000000, then no extended attributes are defined for the file.

Reserved (ULONG) - input
Reserved and must be set to zero.
rc (USHORT) - return
Return code descriptions are:
• NO_ERROR 2
  ERROR_FILE_NOT_FOUND
  3
  ERROR_PATH_NOT_FOUND
  4
  ERROR_TOO_MANY_OPEN_FILES
  5
  ERROR_ACCESS_DENIED
  12
  ERROR_INVALID_ACCESS
  26
  ERROR_NOT_DOS_DISK
  32
  ERROR_SHARING_VIOLATION
  36
  ERROR_SHARING_BUFFER_EXCEEDED
  82
  ERROR_CANNOT_MAKE
  87
  ERROR_INVALID_PARAMETER
  108
  ERROR_DRIVE_LOCKED
  110
  ERROR_OPEN_FAILED
  112
  ERROR_DISK_FULL
  206
  ERROR_FILENAME_EXCED_RANGE
  231
  ERROR_PIPE_BUSY
  99
  ERROR_DEVICE_IN_USE
  Remarks

  A successful DosOpen2 request for a file returns a handle to access the file. The read/write pointer is set at the first byte of the file. The pointer's position may be changed by a DosChgFilePtr request or by read and write operations on the file.

  The file's date and time can be queried by calling DosQFileInfo, and is set by calling DosSetFileInfo.

  FileAttribute sets attribute bits for the file object. Attributes of an existing file can be queried and set by DosQFileMode and DosSetFileMode. A file's read-only attribute may also be set with the OS/2 ATTRIB command.

  FileAttribute cannot be set to Volume Label. Volume labels cannot be opened. DosSetFSInfo may be issued with a logical drive number to set volume label information.

  The FileSize parameter affects the size of the file only when the file is a new file or a replacement for an existing one. If an existing file is simply opened, FileSize is ignored. DosNewSize may be called to change the existing file's size.

  The value in FileSize is a recommended size for the file. If allocation of the full size fails, the open may still succeed. The file system makes a reasonable attempt to allocate the new size in as nearly contiguous an area as possible on the medium. When the file size is extended, the value of the new bytes is undefined.

  The DASD Open bit provides direct access to an entire disk or diskette volume, independent of the file system. This mode of opening the volume currently mounted on the drive returns a handle to the caller, which represents the logical volume as a single file. The caller specifies this handle with a DosDevIOCtl Category 8 Function 0 request to block other processes from accessing the logical volume.

  The file handle state bits can be set by the DosOpen2 and DosSetFHandState requests. An application can query the file handle state bits as well as the rest of the Open Mode field, by calling DosQFHandState.

  Extended attributes can be set by an EAOP structure in EABuf when creating a file, replacing an existing file, or truncating an existing file. No extended attributes are set when simply opening an existing file.

  A replace operation is logically equivalent to atomically deleting and re-creating the file. This means that any extended attributes associated with the file are also deleted before the file is re-created.

  
  Family API Considerations

  Some options operate differently in the DOS mode than in the OS/2 mode. Therefore, the following restrictions apply to DosOpen when coding for the DOS mode:

  o

  OpenMode restrictions:

  • The high word of OpenMode is ignored and is not error checked.
    
  • Handles returned in response to DASD open are valid only for DosDevIOCtl.
    
  • Inheritance flag is not supported in DOS 2.X.
    
  • Write-Through flag must be set to zero.
    
  • Fail-errors flag must be set to zero.
    
  • Sharing mode field has meaning only if Sharing is loaded in DOS 3.X, ignored if Sharing is not loaded. Sharing mode is not supported in DOS 2.X.
    
  • Access mode field has meaning only if Sharing is loaded in DOS 3.X, ignored if Sharing is not loaded. Access mode field is not supported in DOS 2.X.
  o
  Access mode is valid only if Sharing is loaded.

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