'\" t
.\"     Title: blk_queue_merge_bvec
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: May 2018
.\"    Manual: Block Devices
.\"    Source: Kernel Hackers Manual 3.16.56
.\"  Language: English
.\"
.TH "BLK_QUEUE_MERGE_BVEC" "9" "May 2018" "Kernel Hackers Manual 3\&.16\&" "Block Devices"
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.SH "NAME"
blk_queue_merge_bvec \- set a merge_bvec function for queue
.SH "SYNOPSIS"
.HP \w'void\ blk_queue_merge_bvec('u
.BI "void blk_queue_merge_bvec(struct\ request_queue\ *\ " "q" ", merge_bvec_fn\ *\ " "mbfn" ");"
.SH "ARGUMENTS"
.PP
\fIq\fR
.RS 4
queue
.RE
.PP
\fImbfn\fR
.RS 4
merge_bvec_fn
.RE
.SH "DESCRIPTION"
.PP
Usually queues have static limitations on the max sectors or segments that we can put in a request\&. Stacking drivers may have some settings that are dynamic, and thus we have to query the queue whether it is ok to add a new bio_vec to a bio at a given offset or not\&. If the block device has such limitations, it needs to register a merge_bvec_fn to control the size of bio\*(Aqs sent to it\&. Note that a block device *must* allow a single page to be added to an empty bio\&. The block device driver may want to use the
\fBbio_split\fR
function to deal with these bio\*(Aqs\&. By default no merge_bvec_fn is defined for a queue, and only the fixed limits are honored\&.
.SH "COPYRIGHT"
.br