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.

SEE ALSO

bp_mapin(9F), buf(9S)


Writing Device Drivers

August 22, 2023 BIOMODIFIED(9F)