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    Subject[PATCH 13/31] SYSFS: Allow boot time switching between deprecated and modern sysfs layout
    Date
    From: Andi Kleen <ak@linux.intel.com>

    I have some systems which need legacy sysfs due to old tools that are
    making assumptions that a directory can never be a symlink to another
    directory, and it's a big hazzle to compile separate kernels for them.

    This patch turns CONFIG_SYSFS_DEPRECATED into a run time option
    that can be switched on/off the kernel command line. This way
    the same binary can be used in both cases with just a option
    on the command line.

    The old CONFIG_SYSFS_DEPRECATED_V2 option is still there to set
    the default. I kept the weird name to not break existing
    config files.

    Also the compat code can be still completely disabled by undefining
    CONFIG_SYSFS_DEPRECATED_SWITCH -- just the optimizer takes
    care of this now instead of lots of ifdefs. This makes the code
    look nicer.

    v2: This is an updated version on top of Kay's patch to only
    handle the block devices. I tested it on my old systems
    and that seems to work.

    Cc: axboe@kernel.dk
    Signed-off-by: Andi Kleen <ak@linux.intel.com>
    Cc: Kay Sievers <kay.sievers@vrfy.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    Documentation/kernel-parameters.txt | 9 +++++++++
    block/genhd.c | 7 ++-----
    drivers/base/class.c | 4 ++--
    drivers/base/core.c | 26 +++++++++++++++++---------
    fs/partitions/check.c | 19 +++++++++----------
    include/linux/device.h | 7 +++++++
    init/Kconfig | 26 ++++++++++++++++++++++----
    7 files changed, 68 insertions(+), 30 deletions(-)

    diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    index 3d854c9..67fa3fd 100644
    --- a/Documentation/kernel-parameters.txt
    +++ b/Documentation/kernel-parameters.txt
    @@ -2365,6 +2365,15 @@ and is between 256 and 4096 characters. It is defined in the file

    switches= [HW,M68k]

    + sysfs.deprecated=0|1 [KNL]
    + Enable/disable old style sysfs layout for old udev
    + on older distributions. When this option is enabled
    + very new udev will not work anymore. When this option
    + is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
    + in older udev will not work anymore.
    + Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
    + the kernel configuration.
    +
    sysrq_always_enabled
    [KNL]
    Ignore sysrq setting - this boot parameter will
    diff --git a/block/genhd.c b/block/genhd.c
    index 59a2db6..4e28a84 100644
    --- a/block/genhd.c
    +++ b/block/genhd.c
    @@ -22,9 +22,7 @@
    #include "blk.h"

    static DEFINE_MUTEX(block_class_lock);
    -#ifndef CONFIG_SYSFS_DEPRECATED
    struct kobject *block_depr;
    -#endif

    /* for extended dynamic devt allocation, currently only one major is used */
    #define MAX_EXT_DEVT (1 << MINORBITS)
    @@ -803,10 +801,9 @@ static int __init genhd_device_init(void)

    register_blkdev(BLOCK_EXT_MAJOR, "blkext");

    -#ifndef CONFIG_SYSFS_DEPRECATED
    /* create top-level block dir */
    - block_depr = kobject_create_and_add("block", NULL);
    -#endif
    + if (!sysfs_deprecated)
    + block_depr = kobject_create_and_add("block", NULL);
    return 0;
    }

    diff --git a/drivers/base/class.c b/drivers/base/class.c
    index 1078969..9c63a56 100644
    --- a/drivers/base/class.c
    +++ b/drivers/base/class.c
    @@ -184,9 +184,9 @@ int __class_register(struct class *cls, struct lock_class_key *key)
    if (!cls->dev_kobj)
    cls->dev_kobj = sysfs_dev_char_kobj;

    -#if defined(CONFIG_SYSFS_DEPRECATED) && defined(CONFIG_BLOCK)
    +#if defined(CONFIG_BLOCK)
    /* let the block class directory show up in the root of sysfs */
    - if (cls != &block_class)
    + if (!sysfs_deprecated || cls != &block_class)
    cp->class_subsys.kobj.kset = class_kset;
    #else
    cp->class_subsys.kobj.kset = class_kset;
    diff --git a/drivers/base/core.c b/drivers/base/core.c
    index 6cf9069..f7f906f 100644
    --- a/drivers/base/core.c
    +++ b/drivers/base/core.c
    @@ -26,6 +26,19 @@
    #include "base.h"
    #include "power/power.h"

    +#ifdef CONFIG_SYSFS_DEPRECATED
    +#ifdef CONFIG_SYSFS_DEPRECATED_V2
    +long sysfs_deprecated = 1;
    +#else
    +long sysfs_deprecated = 0;
    +#endif
    +static __init int sysfs_deprecated_setup(char *arg)
    +{
    + return strict_strtol(arg, 10, &sysfs_deprecated);
    +}
    +early_param("sysfs.deprecated", sysfs_deprecated_setup);
    +#endif
    +
    int (*platform_notify)(struct device *dev) = NULL;
    int (*platform_notify_remove)(struct device *dev) = NULL;
    static struct kobject *dev_kobj;
    @@ -617,14 +630,13 @@ static struct kobject *get_device_parent(struct device *dev,
    struct kobject *parent_kobj;
    struct kobject *k;

    -#ifdef CONFIG_SYSFS_DEPRECATED
    /* block disks show up in /sys/block */
    - if (dev->class == &block_class) {
    + if (sysfs_deprecated && dev->class == &block_class) {
    if (parent && parent->class == &block_class)
    return &parent->kobj;
    return &block_class.p->class_subsys.kobj;
    }
    -#endif
    +
    /*
    * If we have no parent, we live in "virtual".
    * Class-devices with a non class-device as parent, live
    @@ -707,11 +719,9 @@ static int device_add_class_symlinks(struct device *dev)
    goto out_subsys;
    }

    -#ifdef CONFIG_SYSFS_DEPRECATED
    /* /sys/block has directories and does not need symlinks */
    - if (dev->class == &block_class)
    + if (sysfs_deprecated && dev->class == &block_class)
    return 0;
    -#endif

    /* link in the class directory pointing to the device */
    error = sysfs_create_link(&dev->class->p->class_subsys.kobj,
    @@ -738,10 +748,8 @@ static void device_remove_class_symlinks(struct device *dev)
    if (dev->parent && device_is_not_partition(dev))
    sysfs_remove_link(&dev->kobj, "device");
    sysfs_remove_link(&dev->kobj, "subsystem");
    -#ifdef CONFIG_SYSFS_DEPRECATED
    - if (dev->class == &block_class)
    + if (sysfs_deprecated && dev->class == &block_class)
    return;
    -#endif
    sysfs_delete_link(&dev->class->p->class_subsys.kobj, &dev->kobj, dev_name(dev));
    }

    diff --git a/fs/partitions/check.c b/fs/partitions/check.c
    index 79fbf3f..137bf97 100644
    --- a/fs/partitions/check.c
    +++ b/fs/partitions/check.c
    @@ -513,14 +513,14 @@ void register_disk(struct gendisk *disk)

    if (device_add(ddev))
    return;
    -#ifndef CONFIG_SYSFS_DEPRECATED
    - err = sysfs_create_link(block_depr, &ddev->kobj,
    - kobject_name(&ddev->kobj));
    - if (err) {
    - device_del(ddev);
    - return;
    + if (!sysfs_deprecated) {
    + err = sysfs_create_link(block_depr, &ddev->kobj,
    + kobject_name(&ddev->kobj));
    + if (err) {
    + device_del(ddev);
    + return;
    + }
    }
    -#endif
    disk->part0.holder_dir = kobject_create_and_add("holders", &ddev->kobj);
    disk->slave_dir = kobject_create_and_add("slaves", &ddev->kobj);

    @@ -737,8 +737,7 @@ void del_gendisk(struct gendisk *disk)
    kobject_put(disk->part0.holder_dir);
    kobject_put(disk->slave_dir);
    disk->driverfs_dev = NULL;
    -#ifndef CONFIG_SYSFS_DEPRECATED
    - sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
    -#endif
    + if (!sysfs_deprecated)
    + sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
    device_del(disk_to_dev(disk));
    }
    diff --git a/include/linux/device.h b/include/linux/device.h
    index 516feca..dd48953 100644
    --- a/include/linux/device.h
    +++ b/include/linux/device.h
    @@ -751,4 +751,11 @@ do { \
    MODULE_ALIAS("char-major-" __stringify(major) "-" __stringify(minor))
    #define MODULE_ALIAS_CHARDEV_MAJOR(major) \
    MODULE_ALIAS("char-major-" __stringify(major) "-*")
    +
    +#ifdef CONFIG_SYSFS_DEPRECATED
    +extern long sysfs_deprecated;
    +#else
    +#define sysfs_deprecated 0
    +#endif
    +
    #endif /* _DEVICE_H_ */
    diff --git a/init/Kconfig b/init/Kconfig
    index 137609f..d742b6f 100644
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -660,8 +660,12 @@ config SYSFS_DEPRECATED
    depends on SYSFS
    default n
    help
    - This option switches the layout of the "block" class devices, to not
    - show up in /sys/class/block/, but only in /sys/block/.
    + This option adds code that switches the layout of the "block" class
    + devices, to not show up in /sys/class/block/, but only in
    + /sys/block/.
    +
    + This switch is only active when the sysfs.deprecated=1 boot option is
    + passed or the SYSFS_DEPRECATED_V2 option is set.

    This option allows new kernels to run on old distributions and tools,
    which might get confused by /sys/class/block/. Since 2007/2008 all
    @@ -672,8 +676,22 @@ config SYSFS_DEPRECATED
    option enabled.

    Only if you are using a new kernel on an old distribution, you might
    - need to say Y here. Never say Y, if the original kernel, that came
    - with your distribution, has not set this option.
    + need to say Y here.
    +
    +config SYSFS_DEPRECATED_V2
    + bool "enabled deprecated sysfs features by default"
    + default n
    + depends on SYSFS
    + depends on SYSFS_DEPRECATED
    + help
    + Enable deprecated sysfs by default.
    +
    + See the CONFIG_SYSFS_DEPRECATED option for more details about this
    + option.
    +
    + Only if you are using a new kernel on an old distribution, you might
    + need to say Y here. Even then, odds are you would not need it
    + enabled, you can always pass the boot option if absolutely necessary.

    config RELAY
    bool "Kernel->user space relay support (formerly relayfs)"
    --
    1.7.2


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