DCMD_FSYS_DIRECT

Synopsis:

#include <sys/dcmd_blk.h>

#define DCMD_FSYS_DIRECT_IO   __DIOT(_DCMD_FSYS,  15, struct fs_directio)

Arguments to devctl():

Argument	Value
`filedes`	A file descriptor that you obtained by opening the device.
`dcmd`	DCMD_FSYS_DIRECT_IO
`dev_data_ptr`	A pointer to a struct fs_directio (see below)
`n_bytes`	`sizeof(struct fs_directio)`
`dev_info_ptr`	NULL

Description:

This command performs a direct I/O operation on a file.

Input:

The fs_directio structure is defined in <sys/dcmd_blk.h> as follows:

struct fs_directio {
        off64_t         offset;
        uint32_t        nbytes;
        uint32_t        flags;
        paddr_t         paddr;
        caddr_t         vaddr;
};

The members include:

offset

The offset in the file to start the operation at.

nbytes

The number of bytes you want to read or write.

flags

The type of operation; one of:

FS_DIO_READ — read-only
FS_DIO_WRITE — write-only

You can OR either of these with FS_DIO_SYNC, to indicate that subsequent operations are complete only when the data has been successfully transferred.

paddr

The physical address of where to read or write the data.

vaddr

The virtual address of where to read or write the data.

Output:

None.

Example:

struct fs_directio		dio;

/* Send a zero-byte read to see if direct I/O is available on the fd: */

memset(&dio, 0, sizeof dio);
dio.flags = _IO_FLAG_RD;
if (devctl(fd, DCMD_FSYS_DIRECT_IO, &dio, sizeof dio, 0) == EOK)
{
  /* Direct I/O is supported. */
}