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Update the physio man page to better reflect reality.

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PR:		docs/30603
Reviewed by:	phk
MFC after:	3 days
This commit is contained in:
Josef Karthauser 2002-02-05 21:32:57 +00:00
parent 551858f0b0
commit e105123179
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=90265
1 changed files with 14 additions and 37 deletions
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51
share/man/man9/physio.9
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@ -54,16 +54,12 @@ The
.Fn physio
is a helper function typically called from character device read and write
routines to start I/O on a user process buffer.
It calls back on the
provided
.Fa strategy
routine one or more times to complete the transfer described by
.Fa uio .
The maximum amount of data to transfer with each call to
.Fa strategy
is determined by the
.Fa minphys
routine.
The maximum amount of data to transfer with each call
is determined by:
.Bd -literal
dev->si_iosize_max
.Ed
.Pp
Since
.Fa uio
normally describes user space addresses,
@ -74,38 +70,11 @@ flag on the process.
.Fn physio
always awaits the completion of the entire requested transfer before
returning, unless an error condition is detected earlier.
In all cases,
the buffer passed in
.Fa bp
is locked (marked as
.Dq busy )
for the duration of the entire transfer.
.Pp
A break-down of the arguments follows:
.Bl -tag -width indent
.It Fa strategy
The device strategy routine to call for each chunk of data to initiate
device I/O.
.It Fa bp
The buffer to use with the strategy routine.
The buffer flags will have
.Dv B_BUSY ,
and
.Dv B_PHYS
set when passed to the strategy routine.
If
.Dv NULL ,
a buffer is allocated from a system pool.
.It Fa dev
The device number identifying the device to interact with.
.It Fa flags
Direction of transfer; the only valid settings are
.Dv B_READ
or
.Dv B_WRITE .
.It Fa minphys
A device specific routine called to determine the maximum transfer size
that the device's strategy routine can handle.
.It Fa uio
The description of the entire transfer as requested by the user process.
Currently, the results of passing a
@ -139,3 +108,11 @@ condition.
.Sh SEE ALSO
.Xr read 2 ,
.Xr write 2
.Sh HISTORY
The
.Xr physio 9
manual page is originally from NetBSD with minor changes for applicability
with FreeBSD.
.Pp
The physio(9) call has been completely re-written for providing higher
I/O performance, and better paging performance.