illumos: manual page: biomodified.9f

BIOMODIFIED(9F) Kernel Functions for Drivers BIOMODIFIED(9F)

NAME

biomodified - check if a buffer is modified

SYNOPSIS

#include <sys/ddi.h>
#include <sys/sunddi.h>

int biomodified(struct buf *bp);

INTERFACE LEVEL

illumos DDI specific (illumos DDI).

PARAMETERS

bp
Pointer to the buffer header structure.

DESCRIPTION

The biomodified() function returns status to indicate if the buffer is
modified. The biomodified() function is only supported for paged-I/O
request, that is the B_PAGEIO flag must be set in the b_flags field of
the buf(9S) structure. The biomodified() function will check the memory
pages associated with this buffer whether the Virtual Memory system's
modification bit is set. If at least one of these pages is modified, the
buffer is indicated as modified. A filesystem will mark the pages
unmodified when it writes the pages to the backing store. The
biomodified() function can be used to detect any modifications to the
memory pages while I/O is in progress.

A device driver can use biomodified() for disk mirroring. An application
is allowed to mmap a file which can reside on a disk which is mirrored
by multiple submirrors. If the file system writes the file to the backing
store, it is written to all submirrors in parallel. It must be ensured
that the copies on all submirrors are identical. The biomodified()
function can be used in the device driver to detect any modifications to
the buffer by the user program during the time the buffer is written to
multiple submirrors.

RETURN VALUES

The biomodified() function returns the following values:

1
Buffer is modified.

0
Buffer is not modified.

-1
Buffer is not used for paged I/O request.

CONTEXT

biomodified() can be called from any context.