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Message-Id: <1203670297.4995.12.camel@queen.suse.de>
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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