'\" t
.\"     Title: blk_stack_limits
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: January 2017
.\"    Manual: Block Devices
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "BLK_STACK_LIMITS" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Block Devices"
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.SH "NAME"
blk_stack_limits \- adjust queue_limits for stacked devices
.SH "SYNOPSIS"
.HP \w'int\ blk_stack_limits('u
.BI "int blk_stack_limits(struct\ queue_limits\ *\ " "t" ", struct\ queue_limits\ *\ " "b" ", sector_t\ " "start" ");"
.SH "ARGUMENTS"
.PP
\fIt\fR
.RS 4
the stacking driver limits (top device)
.RE
.PP
\fIb\fR
.RS 4
the underlying queue limits (bottom, component device)
.RE
.PP
\fIstart\fR
.RS 4
first data sector within component device
.RE
.SH "DESCRIPTION"
.PP
This function is used by stacking drivers like MD and DM to ensure that all component devices have compatible block sizes and alignments\&. The stacking driver must provide a queue_limits struct (top) and then iteratively call the stacking function for all component (bottom) devices\&. The stacking function will attempt to combine the values and ensure proper alignment\&.
.PP
Returns 0 if the top and bottom queue_limits are compatible\&. The top device\*(Aqs block sizes and alignment offsets may be adjusted to ensure alignment with the bottom device\&. If no compatible sizes and alignments exist, \-1 is returned and the resulting top queue_limits will have the misaligned flag set to indicate that the alignment_offset is undefined\&.
.SH "COPYRIGHT"
.br