Bug 30603

I am currently having a look into this problem.  A patch should be 
soon submitted.  This issue will take a bit time for me, but it will
be fixed hopefully, before FreeBSD 4.5 is released.

The structure of the physio() routine has been changed from:
(as found in the src/sys/sys/buf.h header file)

OLD: physio(void (*strategy)(struct buf *), struct buf *bp, dev_t dev, 
     int flags, u_int (*minphys)(struct buf *), struct uio *uio);

NEW: int physio (dev_t dev, struct uio *uio, int ioflag);

The initial change was done by phk@FreeBSD.org, as he refered to it 
as "wash-and-clean of code".  In other words, this routine has been
given a makeover since the 3.5.1 release..

Saying that, this change was made 2 years ago!, and no-one noticed
it till now.. thanks to chris..

The following changes were made: (according to the cvs log of revision
1.81)
(I am refering to the src/sys/sys/buf.h file.. others had to be updated
too..)

o Let physio take read/write compatible args and have it use
  uio->uio_rw to determine the direction.

o physread/physwrite are now #defines for physio

o Remove the inversly name minphys() routine, dev->si_iosize_max
  takes over.

o physio() always uses pbufs.

o Fix the check for non page-aligned transfers, now only unaligned
  transfers largen than (MAXPHYS - PAGE_SIZE) get fragmented (only
  interesting for tapes using max blocksize).

So, in a nutshell, the physio(9) man page needs a re-write, which I will
do ASAP :)

regards,
- Hiten
- <hiten@uk.FreeBSD.org>

-- 
SSH Fingerprint:
1024 45:a5:9c:f2:fb:07:da:70:18:02:0b:f3:63:f1:7a:a6 hitenp@hpdi.ath.cx

I finally got time to fix this problem, and
make a patch to the physio(9) man page. Well,
hear it is.  I think this should do.

I have made all the neccessary changes, as well
as add a HISTORY section.

A copy of this diff is also available at:
http://www.pittgoth.com/~hiten/diffs/physio.9.diff

If there is any problems with this diff, please
do not hesitate to contact me. Feedback is also
very much appreciated.

Regards,
 - Hiten
 - <hiten@uk.FreeBSD.org>
 
--- physio.9	Wed Dec 26 23:14:04 2001
+++ physio.9.new	Wed Jan 30 06:45:02 2002
@@ -54,16 +54,12 @@
 .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 @@
 .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 @@
 .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.

Comment 3 joe 2002-02-05 21:34:32 UTC

State Changed
From-To: open->closed

I've committed the updated man page to -current, will MFC in a few days.