geteblk(D3) geteblk(D3)
NAME
geteblk - get an empty buffer
SYNOPSIS
#include <sys/types.h>
#include <sys/buf.h>
#include <sys/ddi.h>
buf_t *geteblk(void);
DESCRIPTION
geteblk retrieves a buffer [see buf(D4)] from the buffer cache
and returns a pointer to the buffer header. If a buffer is
not available, geteblk sleeps until one is available.
Return Values
A pointer to the buffer header structure is returned.
USAGE
When the driver strategy(D2) routine receives a buffer header
from the kernel, all the necessary members are already
initialized. However, when a driver allocates buffers for its
own use, it must set up some of the members before calling its
strategy routine.
The following list describes the state of these members when
the buffer header is received from geteblk:
b_flags is set to indicate the transfer is from
the user's buffer to the kernel. The
driver must set the B_READ flag if the
transfer is from the kernel to the user's
buffer.
b_edev is set to NODEV and must be initialized by
the driver.
b_bcount is set to 1024.
b_un.b_addr is set to the buffer's virtual address.
b_blkno is not initialized by geteblk, and must be
initialized by the driver
Typically, block drivers do not allocate buffers. The buffer
is allocated by the kernel, and the associated buffer header
is used as an argument to the driver strategy routine.
Copyright 1994 Novell, Inc. Page 1
geteblk(D3) geteblk(D3)
However, to implement some special features, such as ioctl(D2)
commands that perform I/O, the driver may need its own buffer
space. The driver can get the buffer space from the system by
using geteblk or ngeteblk(D3). If the driver chooses to use
its own memory for the buffer, it can allocate a buffer header
only using getrbuf(D3).
Buffers allocated via geteblk must be freed using either
brelse(D3) or biodone(D3).
Level
Base only.
Synchronization Constraints
Can sleep.
Driver-defined basic locks and read/write locks may not be
held across calls to this function.
Driver-defined sleep locks may be held across calls to this
function.
REFERENCES
biodone(D3), biowait(D3), brelse(D3), buf(D4), ngeteblk(D3)
NOTICES
Portability
All processors
Applicability
ddi: 1, 2, 3, 4, 5, 5mp, 6, 6mp, 7, 7mp
Copyright 1994 Novell, Inc. Page 2