7.7. DF_UIO -- User-Defined I/O

• 7.7.1. DF_UIO Definition
• 7.7.2. DF_UIO Field Descriptions
• 7.7.3. Usage Rules
• Specifying User I/O for fx_sendfax( )
• Specifying User I/O for fx_rcvfax2( )

The DF_UIO structure contains pointers to user-defined functions that replace the standard I/O functions read( ), write( ) and lseek( ). This structure is passed to fx_setuio( ).

The user-defined I/O functions are passed the same arguments and must specify the same return type as the standard I/O functions. The fax library stores the pointers to the user-defined read, write and seek functions.

7.7.1. DF_UIO Definition

The DF_UIO structure consists of the following fields.

typedef struct df_uio {  
     int (*u_read)( );     /* User defined replacement for read( ) */  
     int (*u_write)( );    /* User defined replacement for write( ) */  
     long (*u_seek)( );    /* User defined replacement for lseek( ) */  
};




7.7.2. DF_UIO Field Descriptions

The DF_UIO fields are described in Table 20. DF_UIO Fields.

Table 20. DF_UIO Fields

Field	Description
u_read	A pointer to the user-defined read( ) function.
u_write	A pointer to the user-defined write( ) function.
u_seek	A pointer to the user-defined lseek( ) function.

7.7.3. Usage Rules

The following rules apply to the use of the DF_UIO structure:

• specifying user I/O for fx_sendfax( )
• specifying user I/O for fx_rcvfax2( )

Specifying User I/O for fx_sendfax( )

To specify user-defined I/O functions for use in sending a fax, you must "OR" the io_type field of the appropriate DF_IOTT structure with IO_UIO.

The fax library then calls the user-defined seek and read functions when processing the DF_IOTT structure. The file descriptor argument passed to the user-defined functions is the value specified in the io_fhandle field of the DF_IOTT structure.

NOTE:

In an array of DF_IOTT structures passed to the fx_sendfax( ) function, the user-defined I/O functions are only called for those structures whose IO_UIO bit is set in the io_type field. The standard I/O functions are used for all other DF_IOTT structures.

Specifying User I/O for fx_rcvfax2( )

To specify user-defined I/O functions for use in receiving a fax, you must "OR" the rcvflag argument of the fx_rcvfax2( ) function with the IO_UIO bit.

The fax library then calls the user-defined seek and write functions every time fax data is to be written to the I/O device. The file descriptor passed to the user-defined I/O functions is the fd argument to the fx_rcvfax2( ) function.

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