DCMD_ALL_FADVISE

Synopsis:

#include <sys/dcmd_all.h>

#define DCMD_ALL_FADVISE __DIOT(_DCMD_ALL, 6, struct _fadvise)

Arguments to devctl():

Argument	Value
`filedes`	A file descriptor that you obtained by opening the device.
`dcmd`	DCMD_ALL_FADVISE
`dev_data_ptr`	A pointer to a struct _fadvise with the advice filled in (see below).
`n_bytes`	`sizeof(struct _fadvise)`
`dev_info_ptr`	NULL

Description:

This command passes file advice to the filesystem. Clients usually use the posix_fadvise() cover function to generate this request:

posix_fadvise(fd, offset, len, advice);

Input:

A pointer to a struct _fadvise with the advice filled in. This structure is defined as:

struct _fadvise {
        int                     advice;
        int                     spare;
        off64_t                 offset;
        off64_t                 len;
};

The members include the following:

advice

The advice you want to give; one of:

POSIX_FADV_NORMAL — the application has no advice to give on its behavior with respect to the specified data. This is the default characteristic if no advice is given for an open file.
POSIX_FADV_SEQUENTIAL — the application expects to access the specified data sequentially from lower offsets to higher offsets.
POSIX_FADV_RANDOM — the application expects to access the specified data in a random order.
POSIX_FADV_WILLNEED — the application expects to access the specified data in the near future.
POSIX_FADV_DONTNEED — the application expects that it will not access the specified data in the near future.
POSIX_FADV_NOREUSE — the application expects to access the specified data once and then not reuse it thereafter.

spare

Not used; set it to zero.

offset

The offset of the data that you want to provide advice about.

len

The length of the data.

Output:

None.

Example:

struct _fadvise		a;

a.advice = advice;
a.offset = offset;
a.len = len;
a.spare = 0;

if(devctl(fd, DCMD_ALL_FADVISE, &a, sizeof a, NULL) != EOK)
{
   /* Error */
}