DCMD_FSYS_DIRECT

Synopsis:

#include <sys/dcmd_blk.h>

#define DCMD_FSYS_DIRECT_IO      __DIOT(_DCMD_FSYS, 15, struct fs_directio)
#define DCMD_FSYS_DIRECT_IO_IOV  __DIOT(_DCMD_FSYS, 38, struct fs_directio_iov)
#define DCMD_FSYS_DIRECT_IO_OLD  __DIOT(_DCMD_FSYS, 15, struct fs_directio_old)

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`	A pointer to a 32-bit signed integer. On success, the devctl() call populates this buffer with the number of bytes successfully transferred. Pass NULL if you do not want this information.

Description:

The DCMD_FSYS_DIRECT_IO command performs a direct I/O operation on a file. DCMD_FSYS_DIRECT_IO_IOV allows DCMD_FSYS_DIRECT_IO to be used when the client's buffers are not contiguous in memory.

Input:

fs_directio

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;
        paddr64_t       paddr;
        uint64_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 the above with zero or one or both of the following:

FS_DIO_SYNC — subsequent operations are complete only when the data has been successfully transferred
FS_DIO_MAP_PHYS — map physical memory

paddr

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

vaddr

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

fs_directio_iov

You use the fs_directio_iov structure when the client's buffers are not contiguous in memory. To use this form of the structure, use DCMD_FSYS_DIRECT_IO_IOV.

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

struct fs_directio_iov {
        off64_t         offset;
        _Uint32t        nbytes;
        _Uint32t        flags;
        _Uint32t        niov;
        __FLEXARY(struct __iovec64, iov);
};

The offset and flags members are as for fs_directio.

nbytes: The number of bytes you want to read or write. It's the sum of the lengths of each IOV specified by iov.
nbytes: The number of bytes you want to read or write.
niov: The number of elements in the iov array.
iov: An array of struct __iovec64. The _iov_base member of the iov holds either the paddr or the vaddr, depending on whether FS_DIO_MAP_PHYS is set in flags.

fs_directio_old

The fs_directio_old structure is similar to fs_directio, except that the paddr member is of type paddr32_t, and the vaddr member is of type uint32_t. If you want this form of the structure, use DCMD_FSYS_DIRECT_IO_OLD.

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. */
}

DCMD_FSYS_DIRECT_IO