Date:	Fri, 22 Feb 2008 09:51:37 +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 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.

> 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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