by Sourabh Jain

[permalink] [raw]

Subject: Re: [PATCH v4 6/6] powerpc/fadump: sysfs for fadump memory reservation

On 12/6/19 6:18 PM, Greg KH wrote:
> On Fri, Dec 06, 2019 at 05:54:34PM +0530, Sourabh Jain wrote:
>> Add a sys interface to allow querying the memory reserved by FADump for
>> saving the crash dump.
>>
>> Also added Documentation/ABI for the new sysfs file.
>>
>> Signed-off-by: Sourabh Jain <[email protected]>
>> ---
>> Documentation/ABI/testing/sysfs-kernel-fadump | 7 +++++++
>> Documentation/powerpc/firmware-assisted-dump.rst | 5 +++++
>> arch/powerpc/kernel/fadump.c | 15 +++++++++++++++
>> 3 files changed, 27 insertions(+)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-kernel-fadump b/Documentation/ABI/testing/sysfs-kernel-fadump
>> index 5d988b919e81..8f7a64a81783 100644
>> --- a/Documentation/ABI/testing/sysfs-kernel-fadump
>> +++ b/Documentation/ABI/testing/sysfs-kernel-fadump
>> @@ -31,3 +31,10 @@ Description: write only
>> the system is booted to capture the vmcore using FADump.
>> It is used to release the memory reserved by FADump to
>> save the crash dump.
>> +
>> +What: /sys/kernel/fadump/mem_reserved
>> +Date: Dec 2019
>> +Contact: [email protected]
>> +Description: read only
>> + Provide information about the amount of memory reserved by
>> + FADump to save the crash dump in bytes.
>> diff --git a/Documentation/powerpc/firmware-assisted-dump.rst b/Documentation/powerpc/firmware-assisted-dump.rst
>> index 365c10209ef3..04993eaf3113 100644
>> --- a/Documentation/powerpc/firmware-assisted-dump.rst
>> +++ b/Documentation/powerpc/firmware-assisted-dump.rst
>> @@ -268,6 +268,11 @@ Here is the list of files under kernel sysfs:
>> be handled and vmcore will not be captured. This interface can be
>> easily integrated with kdump service start/stop.
>>
>> + /sys/kernel/fadump/mem_reserved
>> +
>> + This is used to display the memory reserved by FADump for saving the
>> + crash dump.
>> +
>> /sys/kernel/fadump_release_mem
>> This file is available only when FADump is active during
>> second kernel. This is used to release the reserved memory
>> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
>> index 41a3cda81791..b2af51b7c750 100644
>> --- a/arch/powerpc/kernel/fadump.c
>> +++ b/arch/powerpc/kernel/fadump.c
>> @@ -1357,6 +1357,13 @@ static ssize_t fadump_enabled_show(struct kobject *kobj,
>> return sprintf(buf, "%d\n", fw_dump.fadump_enabled);
>> }
>>
>> +static ssize_t fadump_mem_reserved_show(struct kobject *kobj,
>> + struct kobj_attribute *attr,
>> + char *buf)
>> +{
>> + return sprintf(buf, "%ld\n", fw_dump.reserve_dump_area_size);
>> +}
>> +
>> static ssize_t fadump_register_show(struct kobject *kobj,
>> struct kobj_attribute *attr,
>> char *buf)
>> @@ -1430,6 +1437,10 @@ static struct kobj_attribute enable_attr = __ATTR(enabled,
>> static struct kobj_attribute register_attr = __ATTR(registered,
>> 0644, fadump_register_show,
>> fadump_register_store);
>> +static struct kobj_attribute mem_reserved_attr = __ATTR(mem_reserved,
>> + 0444, fadump_mem_reserved_show,
>> + NULL);
>
> __ATTRI_RO()?
>
>> +
>>
>> DEFINE_SHOW_ATTRIBUTE(fadump_region);
>>
>> @@ -1464,6 +1475,10 @@ static void fadump_init_files(void)
>> pr_err("unable to create release_mem sysfs file (%d)\n",
>> rc);
>> }
>> + rc = sysfs_create_file(fadump_kobj, &mem_reserved_attr.attr);
>> + if (rc)
>> + pr_err("unable to create mem_reserved sysfs file (%d)\n",
>> + rc);
>
> Again, put it in an attribute group, that would have only required one
> line, and not this mess of not cleaning up if something went wrong.

Will make the changes accordingly.

Thanks,
Sourabh Jain

2019-12-07 03:25:27

by Sourabh Jain

[permalink] [raw]

Subject: Re: [PATCH v4 2/6] sysfs: wrap __compat_only_sysfs_link_entry_to_kobj function to change the symlink name

On 12/7/19 12:44 AM, Greg KH wrote:
> On Fri, Dec 06, 2019 at 11:57:53PM +0530, Sourabh Jain wrote:
>>
>>
>> On 12/6/19 6:16 PM, Greg KH wrote:
>>> On Fri, Dec 06, 2019 at 05:54:30PM +0530, Sourabh Jain wrote:
>>>> The __compat_only_sysfs_link_entry_to_kobj function creates a symlink to a
>>>> kobject but doesn't provide an option to change the symlink file name.
>>>>
>>>> This patch adds a wrapper function create_sysfs_symlink_entry_to_kobj that
>>>> extends the __compat_only_sysfs_link_entry_to_kobj functionality which
>>>> allows function caller to customize the symlink name.
>>>>
>>>> Signed-off-by: Sourabh Jain <[email protected]>
>>>> ---
>>>> fs/sysfs/group.c | 28 +++++++++++++++++++++++++---
>>>> include/linux/sysfs.h | 12 ++++++++++++
>>>> 2 files changed, 37 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
>>>> index d41c21fef138..5eb38145b957 100644
>>>> --- a/fs/sysfs/group.c
>>>> +++ b/fs/sysfs/group.c
>>>> @@ -424,6 +424,25 @@ EXPORT_SYMBOL_GPL(sysfs_remove_link_from_group);
>>>> int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
>>>> struct kobject *target_kobj,
>>>> const char *target_name)
>>>> +{
>>>> + return create_sysfs_symlink_entry_to_kobj(kobj, target_kobj,
>>>> + target_name, NULL);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(__compat_only_sysfs_link_entry_to_kobj);
>>>> +
>>>> +/**
>>>> + * create_sysfs_symlink_entry_to_kobj - add a symlink to a kobject pointing
>>>> + * to a group or an attribute
>>>> + * @kobj: The kobject containing the group.
>>>> + * @target_kobj: The target kobject.
>>>> + * @target_name: The name of the target group or attribute.
>>>> + * @symlink_name: The name of the symlink file (target_name will be
>>>> + * considered if symlink_name is NULL).
>>>> + */
>>>> +int create_sysfs_symlink_entry_to_kobj(struct kobject *kobj,
>>>> + struct kobject *target_kobj,
>>>> + const char *target_name,
>>>> + const char *symlink_name)
>>>> {
>>>> struct kernfs_node *target;
>>>> struct kernfs_node *entry;
>>>> @@ -448,12 +467,15 @@ int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
>>>> return -ENOENT;
>>>> }
>>>>
>>>> - link = kernfs_create_link(kobj->sd, target_name, entry);
>>>> + if (!symlink_name)
>>>> + symlink_name = target_name;
>>>> +
>>>> + link = kernfs_create_link(kobj->sd, symlink_name, entry);
>>>> if (IS_ERR(link) && PTR_ERR(link) == -EEXIST)
>>>> - sysfs_warn_dup(kobj->sd, target_name);
>>>> + sysfs_warn_dup(kobj->sd, symlink_name);
>>>>
>>>> kernfs_put(entry);
>>>> kernfs_put(target);
>>>> return PTR_ERR_OR_ZERO(link);
>>>> }
>>>> -EXPORT_SYMBOL_GPL(__compat_only_sysfs_link_entry_to_kobj);
>>>> +EXPORT_SYMBOL_GPL(create_sysfs_symlink_entry_to_kobj);
>>>> diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
>>>> index 5420817ed317..123c6f10333a 100644
>>>> --- a/include/linux/sysfs.h
>>>> +++ b/include/linux/sysfs.h
>>>> @@ -300,6 +300,10 @@ void sysfs_remove_link_from_group(struct kobject *kobj, const char *group_name,
>>>> int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
>>>> struct kobject *target_kobj,
>>>> const char *target_name);
>>>> +int create_sysfs_symlink_entry_to_kobj(struct kobject *kobj,
>>>> + struct kobject *target_kobj,
>>>> + const char *target_name,
>>>> + const char *symlink_name);
>>>
>>> sysfs_create_symlink_entry_to_kobj()?
>>>
>>> I can't remember why we put __compat_only there, perhaps because we do
>>> not want people to really use this unless you really really have to?
>>
>> We don't have much option here. I tried replicating the sysfs files
>> in older patch series but creating symlink at old location is much
>> better approach.
>>
>> The __compat_only_sysfs_link_entry_to_kobj function is pretty generic,
>> unable to understand the reason behind restricting its usage.
>>
>>>
>>> So then keep compat_only here as well?
>>
>> Sure, I will rename the wrapper function.
>>
>> But how about changing the function signature instead of creating
>> a wrapper function?
>>
>> Considering the fact that there are only two places this function
>> has called.
>>
>>>
>>> What breaks if you remove those undocumented sysfs files? What
>>> userspace tool do you have that will even notice?
>>
>> The scripts used in kdump service need those sysfs files to control
>> the dump collection. So we can't just move the sysfs files to the
>> new location.
>
> If you can not change them, then just document them and live with it.
> Why do this extra work to create a symlink for something you will never
> use?

Eventually the scripts will change but I think it is better to have some
overlap time to avoid breaking those scripts.

Thanks,
Sourabh Jain