[rfc/rfa] [1/4] SPU enhancements: preparation

[rfc/rfa] [1/4] SPU enhancements: preparation

[Ulrich Weigand]

Hello,

this is a small fix in preparation for adding extended SPU query support.
Some files in spufs accessed via the spu_proc_xfer_spu routines in
spu-linux-nat.c and gdbserver/spu-low.c are non-seekable.  Currently,
any attempt to access those at non-zero offset results in a failure.

However, that is a problem when trying to use those files via the
target object mechanism.  For example, the target_read routine will
first read a chunk at offset zero (which succeeds, and in fact is
generally sufficient to retrieve the full contents as the non-seekable
files are small).  But then it attempts a second read at an offset
corresponding to the length of the first chunk read, which now fails.

This patch changes spu_proc_xfer_spu to simply return zero (i.e. no
more data available) on any attempt to access a non-seekable spufs
file at non-zero offset.

Tested on spu-elf in conjunction with the other patches.

Bye,
Ulrich


ChangeLog:

	* spu-linux-nat.c (spu_proc_xfer_spu): Do not return failure when
	accessing non-seekable spufs files.

gdbserver/ChangeLog:

	* spu-low.c (spu_proc_xfer_spu): Do not return failure when
	accessing non-seekable spufs files.


diff -urNp gdb-orig/gdb/gdbserver/spu-low.c gdb-head/gdb/gdbserver/spu-low.c
--- gdb-orig/gdb/gdbserver/spu-low.c	2007-05-10 23:34:34.000000000 +0200
+++ gdb-head/gdb/gdbserver/spu-low.c	2007-06-01 19:21:10.212694495 +0200
@@ -248,7 +248,7 @@ spu_proc_xfer_spu (const char *annex, un
       && lseek (fd, (off_t) offset, SEEK_SET) != (off_t) offset)
     {
       close (fd);
-      return -1;
+      return 0;
     }
 
   if (writebuf)
diff -urNp gdb-orig/gdb/spu-linux-nat.c gdb-head/gdb/spu-linux-nat.c
--- gdb-orig/gdb/spu-linux-nat.c	2007-05-09 01:01:49.000000000 +0200
+++ gdb-head/gdb/spu-linux-nat.c	2007-06-01 19:21:10.362672892 +0200
@@ -250,7 +250,7 @@ spu_proc_xfer_spu (const char *annex, gd
       && lseek (fd, (off_t) offset, SEEK_SET) != (off_t) offset)
     {
       close (fd);
-      return -1;
+      return 0;
     }
 
   if (writebuf)
-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com

Re: [rfc/rfa] [1/4] SPU enhancements: preparation

[Daniel Jacobowitz]

On Sat, Jun 02, 2007 at 09:31:11PM +0200, Ulrich Weigand wrote:
> Hello,
> 
> this is a small fix in preparation for adding extended SPU query support.
> Some files in spufs accessed via the spu_proc_xfer_spu routines in
> spu-linux-nat.c and gdbserver/spu-low.c are non-seekable.  Currently,
> any attempt to access those at non-zero offset results in a failure.
> 
> However, that is a problem when trying to use those files via the
> target object mechanism.  For example, the target_read routine will
> first read a chunk at offset zero (which succeeds, and in fact is
> generally sufficient to retrieve the full contents as the non-seekable
> files are small).  But then it attempts a second read at an offset
> corresponding to the length of the first chunk read, which now fails.
> 
> This patch changes spu_proc_xfer_spu to simply return zero (i.e. no
> more data available) on any attempt to access a non-seekable spufs
> file at non-zero offset.
> 
> Tested on spu-elf in conjunction with the other patches.

Seems reasonable to me.

-- 
Daniel Jacobowitz
CodeSourcery

Re: [rfc/rfa] [1/4] SPU enhancements: preparation

[Ulrich Weigand]

> ChangeLog:
> 
> 	* spu-linux-nat.c (spu_proc_xfer_spu): Do not return failure when
> 	accessing non-seekable spufs files.
> 
> gdbserver/ChangeLog:
> 
> 	* spu-low.c (spu_proc_xfer_spu): Do not return failure when
> 	accessing non-seekable spufs files.

I've committed this now.

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com

Re: [rfc/rfa] [1/4] SPU enhancements: preparation

[Mark Kettenis]

> Date: Sat, 2 Jun 2007 21:31:11 +0200 (CEST)
> From: "Ulrich Weigand" <uweigand@de.ibm.com>
> 
> Hello,
> 
> this is a small fix in preparation for adding extended SPU query support.
> Some files in spufs accessed via the spu_proc_xfer_spu routines in
> spu-linux-nat.c and gdbserver/spu-low.c are non-seekable.  Currently,
> any attempt to access those at non-zero offset results in a failure.

Are these files inherently non-seekable (side-effects?) or is this
just a Linux quirk you're trying to work around?

Re: [rfc/rfa] [1/4] SPU enhancements: preparation

[Ulrich Weigand]

Mark Kettenis wrote:
> > this is a small fix in preparation for adding extended SPU query support.
> > Some files in spufs accessed via the spu_proc_xfer_spu routines in
> > spu-linux-nat.c and gdbserver/spu-low.c are non-seekable.  Currently,
> > any attempt to access those at non-zero offset results in a failure.
> 
> Are these files inherently non-seekable (side-effects?) or is this
> just a Linux quirk you're trying to work around?

spufs is a pseudo-filesystem implemented by the Linux kernel 
(similar to the /proc or /sys file systems); files in spufs
aren't actually real files, but provide information about
status of SPU contexts.

Most of those files simply do not support seeking; you can 
only open them, and read their contents out (once).  The
content typically represents a single data item (like the
current SPU event status).

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com