Date:	Fri, 22 Feb 2008 10:05:50 +0100
From:	Thomas Renninger <trenn@...e.de>
To:	Éric Piel <Eric.Piel@...mplin-utc.net>
Cc:	Christoph Hellwig <hch@....de>, dsdt@...gusch.at,
	len.brown@...el.com, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: acpi dsts loading and populate_rootfs

On Fri, 2008-02-22 at 09:51 +0100, Thomas Renninger wrote:
> On Thu, 2008-02-21 at 19:46 +0100, Éric Piel wrote:
> > 12/02/08 06:37, Christoph Hellwig wrote/a écrit:
> > > [skipping the populate_rootfs discussion as it seems you have a better
> > >  handle on that than me]
> > > 
> > > On Sun, Feb 10, 2008 at 12:58:09PM +0100, Eric Piel wrote:
> > >>> And while we're at it the file reading thing in there is utter crap
> > >>> aswell.  You really should be using the firmware loader which works
> > >>> perfectly fine if you initramfs is set up for it.  So please folks,
> > >>> back to the drawing board, do it properly and send it out to lkml
> > >>> for review please.
> > >> Christoph, if you have seen this part of the code, you have probably 
> > >> also read the big fat warning explaining why this cannot be done by 
> > >> firmware loader (ie: userspace cannot be run at this early time, 
> > >> corresponding to acpi_early_init()). However, you probably know the 
> > >> kernel ten times better than me. Could you explain what I misunderstood 
> > >> when writing this warning, and give me some hints about how to use the 
> > >> firmware loader in this case?
> > > 
> > > Sorry, I misparsed the comment.  I took it for the usual I'm too lazy
> > > to put something that could load firmware into initramfs excuse.
> > > 
> > > But thinking about it is there a reason acpi initialization needs to
> > > happen so early that we can't even have userspace in initramfs running?
> 
> Maybe you do not need to activate ACPI mode yet, but you need to load
> the tables early.
Forget that one, the tables are fetched much earlier...

    Thomas
> 
> > Hi,
> > I guess in the complete absolute point of view it's possible to run
> > userspace without ACPI, after all that's what happens if you don't
> > activate ACPI in your kernel. However, so far I've taken the init order
> > as a constant. I'd really prefer not to have to mess with a complete
> > init order reorganization ;-)
> 
> Which is probably a good idea.
> AFAIK Numa, possibly Apic tables must be available quite early.
> 
>    Thomas
> 
> > > 
> > > But if we can't use real userspace this could should at least be written
> > > like the pseudo-userspace in init/do_mounts*.c, using the sys_ syscall
> > > implementations.
> > Yes, thank you very much for the links. Attached is a patch that does
> > this.
> > 
> > > 
> > > As an additional comment the stat + open approach is racy and not a good
> > > idea.  Please just open the file using sys_open, it will tell you
> > > if the file doesn't exist and then use fstat on it to find the
> > > length.  It would also be useful if this kind of code is not hidden
> > > inside acpi but rather done somewhere close to the early init code
> > > because that's where people would expect this kind of nastiness.
> > The attached patch also fixes the stat + open order.
> > 
> > Concerning the place of the code, I've tried to find a better place.
> > However, as acpi_early_init(), from which this function is called, is
> > placed in driver/acpi/ and the acpi_find_dsdt_initrd() function contains
> > quite a few references to acpi code it really looked strange to move it
> > out from the current file. If you still think it make much more sense to
> > move it somewhere else, could you hint me about which you would think it
> > fit better in?
> > 
> > In the mean time, here is a patch which should get the situation already
> > much cleaner. It has been tested on various configs (with and without
> > DSDT). Let me know if you think it is acceptable.
> > 
> > See you,
> > Eric
> > 
> > ---
> > Use userland-like functions for reading the ACPI table
> > 
> > As recommended by Christoph Hellwig, even if we can't rely on the userspace
> > firmware loader so early at boot, at least use normal syscall (as in
> > init/do_mounts_*.c). Similarly, use kfree() instead of ACPI_FREE().
> > 
> > Also, it's recommended to open the file before stating it, to avoid surprises.
> > ---
> >  drivers/acpi/osl.c |   33 +++++++++++++++------------------
> >  1 files changed, 15 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> > index 34b3386..b836305 100644
> > --- a/drivers/acpi/osl.c
> > +++ b/drivers/acpi/osl.c
> > @@ -42,6 +42,7 @@
> >  #include <acpi/acpi_bus.h>
> >  #include <acpi/processor.h>
> >  #include <asm/uaccess.h>
> > +#include <linux/syscalls.h>
> >  
> >  #include <linux/efi.h>
> >  #include <linux/ioport.h>
> > @@ -327,8 +328,7 @@ acpi_os_predefined_override(const struct acpi_predefined_names *init_val,
> >  #ifdef CONFIG_ACPI_CUSTOM_DSDT_INITRD
> >  static struct acpi_table_header *acpi_find_dsdt_initrd(void)
> >  {
> > -	struct file *firmware_file;
> > -	mm_segment_t oldfs;
> > +	int fd;
> >  	unsigned long len, len2;
> >  	struct acpi_table_header *dsdt_buffer, *ret = NULL;
> >  	struct kstat stat;
> > @@ -342,20 +342,21 @@ struct acpi_table_header *acpi_find_dsdt_initrd(void)
> >  	 * But this code must be run before there is any userspace available.
> >  	 * A static/init firmware infrastructure doesn't exist yet...
> >  	 */
> > -	if (vfs_stat(ramfs_dsdt_name, &stat) < 0)
> > -		return ret;
> > +	fd = sys_open(ramfs_dsdt_name, O_RDONLY, 0);
> > +	if (fd < 0)
> > +		return ret; /* No need for warning, no DSDT override is normal */
> > +
> > +	/* There exists 3 different sys_fstat's, all are wrapper to vfs_fstat */
> > +	if (vfs_fstat(fd, &stat) < 0) {
> > +		printk(KERN_ERR PREFIX "Failed to stat %s.\n", ramfs_dsdt_name);
> > +		goto err;
> > +	}
> >  
> >  	len = stat.size;
> >  	/* check especially against empty files */
> >  	if (len <= 4) {
> >  		printk(KERN_ERR PREFIX "Failed: DSDT only %lu bytes.\n", len);
> > -		return ret;
> > -	}
> > -
> > -	firmware_file = filp_open(ramfs_dsdt_name, O_RDONLY, 0);
> > -	if (IS_ERR(firmware_file)) {
> > -		printk(KERN_ERR PREFIX "Failed to open %s.\n", ramfs_dsdt_name);
> > -		return ret;
> > +		goto err;
> >  	}
> >  
> >  	dsdt_buffer = kmalloc(len, GFP_ATOMIC);
> > @@ -364,15 +365,11 @@ struct acpi_table_header *acpi_find_dsdt_initrd(void)
> >  		goto err;
> >  	}
> >  
> > -	oldfs = get_fs();
> > -	set_fs(KERNEL_DS);
> > -	len2 = vfs_read(firmware_file, (char __user *)dsdt_buffer, len,
> > -		&firmware_file->f_pos);
> > -	set_fs(oldfs);
> > +	len2 = sys_read(fd, (char __user *)dsdt_buffer, len);
> >  	if (len2 < len) {
> >  		printk(KERN_ERR PREFIX "Failed to read %lu bytes from %s.\n",
> >  			len, ramfs_dsdt_name);
> > -		ACPI_FREE(dsdt_buffer);
> > +		kfree(dsdt_buffer);
> >  		goto err;
> >  	}
> >  
> > @@ -380,7 +377,7 @@ struct acpi_table_header *acpi_find_dsdt_initrd(void)
> >  			len, ramfs_dsdt_name);
> >  	ret = dsdt_buffer;
> >  err:
> > -	filp_close(firmware_file, NULL);
> > +	sys_close(fd);
> >  	return ret;
> >  }
> >  #endif
> > 

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