Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx> writes:
> Hey Gabriel,
>
> On Mon, 2020-04-13 at 12:53 -0400, Gabriel Krisman Bertazi wrote:
>> A filesystem configuration utility has no way to detect which filename
>> encodings are supported by the running kernel. This means, for
>> instance, mkfs has no way to tell if the generated filesystem will be
>> mountable in the current kernel or not. Also, users have no easy way to
>> know if they can update the encoding in their filesystems and still have
>> something functional in the end.
>>
>> This exposes details of the encodings available in the unicode
>> subsystem, to fill that gap.
>>
>> Cc: Theodore Ts'o <tytso@xxxxxxx>
>> Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
>> Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
>>
>> ---
>> Changes since v1:
>> - Make init functions static. (lkp)
>>
>> Documentation/ABI/testing/sysfs-fs-unicode | 13 +++++
>> fs/unicode/utf8-core.c | 64 ++++++++++++++++++++++
>> fs/unicode/utf8-norm.c | 18 ++++++
>> fs/unicode/utf8n.h | 5 ++
>> 4 files changed, 100 insertions(+)
>> create mode 100644 Documentation/ABI/testing/sysfs-fs-unicode
>>
>> diff --git a/Documentation/ABI/testing/sysfs-fs-unicode b/Documentation/ABI/testing/sysfs-fs-unicode
>> new file mode 100644
>> index 000000000000..15c63367bb8e
>> --- /dev/null
>> +++ b/Documentation/ABI/testing/sysfs-fs-unicode
>> @@ -0,0 +1,13 @@
>> +What: /sys/fs/unicode/latest
>> +Date: April 2020
>> +Contact: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
>> +Description:
>> + The latest version of the Unicode Standard supported by
>> + this kernel
>> +
>
> Missing stop at the end of the sentence?
>
>> +What: /sys/fs/unicode/encodings
>> +Date: April 2020
>> +Contact: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
>> +Description:
>> + List of encodings and corresponding versions supported
>> + by this kernel
>
> Ditto.
>
>> diff --git a/fs/unicode/utf8-core.c b/fs/unicode/utf8-core.c
>> index 2a878b739115..b48e13e823a5 100644
>> --- a/fs/unicode/utf8-core.c
>> +++ b/fs/unicode/utf8-core.c
>> @@ -6,6 +6,7 @@
>> #include <linux/parser.h>
>> #include <linux/errno.h>
>> #include <linux/unicode.h>
>> +#include <linux/fs.h>
>>
>> #include "utf8n.h"
>>
>> @@ -212,4 +213,67 @@ void utf8_unload(struct unicode_map *um)
>> }
>> EXPORT_SYMBOL(utf8_unload);
>>
>> +static ssize_t latest_show(struct kobject *kobj,
>> + struct kobj_attribute *attr, char *buf)
>> +{
>> + int l = utf8version_latest();
>> +
>> + return snprintf(buf, PAGE_SIZE, "UTF-8 %d.%d.%d\n", UNICODE_AGE_MAJ(l),
>> + UNICODE_AGE_MIN(l), UNICODE_AGE_REV(l));
>> +
>> +}
>> +static ssize_t encodings_show(struct kobject *kobj,
>> + struct kobj_attribute *attr, char *buf)
>> +{
>> + int n;
>> +
>> + n = snprintf(buf, PAGE_SIZE, "UTF-8:");
>> + n += utf8version_list(buf + n, PAGE_SIZE - n);
>> + n += snprintf(buf+n, PAGE_SIZE-n, "\n");
>> +
>
> I was wondering how sysfs-compliant this was,
> in terms of one value per attribute.
>
> Although, we do seem to break this on a few cases.
I thought about making it more one-value-per-attribute, by considering
each tuple (encoding,version) a different object. So the structure
would look like:
/sys/fs/unicode/utf-8/<version>/
But it felt completely over-engineered, considering we don't support
anything other than utf-8, and I don't see versions having specific
attributes. But maybe this way is more future-proof.
>
>> + return n;
>> +}
>> +
>> +#define UCD_ATTR(x) \
>> + static struct kobj_attribute x ## _attr = __ATTR_RO(x)
>> +
>> +UCD_ATTR(latest);
>> +UCD_ATTR(encodings);
>> +
>> +static struct attribute *ucd_attrs[] = {
>> + &latest_attr.attr,
>> + &encodings_attr.attr,
>> + NULL,
>> +};
>> +static const struct attribute_group ucd_attr_group = {
>> + .attrs = ucd_attrs,
>> +};
>> +static struct kobject *ucd_root;
>> +
>> +static int __init ucd_init(void)
>> +{
>> + int ret;
>> +
>> + ucd_root = kobject_create_and_add("unicode", fs_kobj);
>> + if (!ucd_root)
>> + return -ENOMEM;
>> +
>> + ret = sysfs_create_group(ucd_root, &ucd_attr_group);
>> + if (ret) {
>> + kobject_put(ucd_root);
>> + ucd_root = NULL;
>> + return ret;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static void __exit ucd_exit(void)
>> +{
>> + kobject_put(ucd_root);
>> +}
>> +
>> +module_init(ucd_init);
>
> This code is not a module, so how about fs_initcall?
Right. for the record, I'm planing to make part of it build as a module
in a future patch to reduce the large footprint of the decoding table on
systems that don't care about it. Will fix on v3.
>
>> +module_exit(ucd_exit)
>> +
>
> I can be wrong, but I see no way to remove it :-)
>
> Thanks,
> Ezequiel
--
Gabriel Krisman Bertazi
