Working with UTF-8 in the kernel
The Unicode standard, of course, defines "code points"; to a first approximation, each code point represents a specific character in a specific language group. How those code points are represented in a stream of bytes — the encoding — is a separate question. Dealing with encodings has challenges of its own, but over the years the UTF-8 encoding has emerged as the preferred way of representing code points in many settings. UTF-8 has the advantages of representing the entire Unicode space while being compatible with ASCII — a valid ASCII string is also valid UTF-8. The developers implementing case independence in the kernel decided to limit it to the UTF-8 encoding, presumably in the hope of solving the problem without going entirely insane.
The API that resulted has two layers: a relatively straightforward set of higher-level operations and the primitives that are used to implement them. We'll start at the top and work our way down.
The high-level UTF-8 API
At a high level, the operations that will be needed can be described fairly simply: validate a string, normalize a string, and compare two strings (perhaps with case folding). There is, though, a catch: the Unicode standard comes in multiple versions (version 12.0.0 was released in early March), and each version is different. The normalization and case-folding rules can change between versions, and not all code points exist in all versions. So, before any of the other operations can be used, a "map" must be loaded for the Unicode version of interest:
struct unicode_map *utf8_load(const char *version);
The given version number can be NULL, in which case the latest supported version will be used and a warning will be emitted. In the ext4 implementation, the Unicode version used with any given filesystem is stored in the superblock. The latest version can be explicitly requested by obtaining its name from utf8version_latest(), which takes no parameters. The return value from utf8_load() is a map pointer that can be used with other operations, or an error-pointer value if something goes wrong. The returned pointer should be freed with utf8_unload() when it is no longer needed.
UTF-8 strings are represented in this interface using the qstr structure defined in <linux/dcache.h>. That reveals an apparent assumption that the use of this API will be limited to filesystem code; that is true for now, but could change in the future.
The single-string operations provided are:
int utf8_validate(const struct unicode_map *um, const struct qstr *str); int utf8_normalize(const struct unicode_map *um, const struct qstr *str, unsigned char *dest, size_t dlen); int utf8_casefold(const struct unicode_map *um, const struct qstr *str, unsigned char *dest, size_t dlen);
All of the functions require the map pointer (um) and the string to be operated upon (str). utf_validate() returns zero if str is a valid UTF-8 string, non-zero otherwise. A call to utf8_normalize() will store a normalized version of str in dest and return the length of the result; utf8_casefold() does case folding as well as normalization. Both functions will return -EINVAL if the input string is invalid or if the result would be longer than dlen.
Comparisons are done with:
int utf8_strncmp(const struct unicode_map *um, const struct qstr *s1, const struct qstr *s2); int utf8_strncasecmp(const struct unicode_map *um, const struct qstr *s1, const struct qstr *s2);
Both functions will compare the normalized versions of s1 and s2; utf8_strncasecmp() will do a case-independent comparison. The return value is zero if the strings are the same, one if they differ, and -EINVAL for errors. These functions only test for equality; there is no "greater than" or "less than" testing.
Moving down
Normalization and case folding require the kernel to gain detailed knowledge of the entire Unicode code point space. There are a lot of rules, and there are multiple ways of representing many code points. The good news is that these rules are packaged, in machine-readable form, with the Unicode standard itself. The bad news is that they take up several megabytes of space.
The UTF-8 patches incorporate these rules by processing the provided files into a data structure in a C header file. A fair amount of space is then regained by removing the information for decomposing Hangul (Korean) code points into their base components, since this is a task that can be done algorithmically as well. There is still a lot of data that has to go into kernel space, though, and it's naturally different for each version of Unicode.
The first step for code wanting to use the lower-level API is to get a pointer to this database for the Unicode version in use. That is done with one of:
struct utf8data *utf8nfdi(unsigned int maxage); struct utf8data *utf8nfdicf(unsigned int maxage);
Here, maxage is the version number of interest, encoded in an integer form from the major, minor, and revision numbers using the UNICODE_AGE() macro. If only normalization is needed, utf8nfdi() should be called; use utf8nfdicf() if case folding is also required. The return value will be an opaque pointer, or NULL if the given version cannot be supported.
Next, a cursor should be set up to track progress working through the string of interest:
int utf8cursor(struct utf8cursor *cursor, const struct utf8data *data, const char *s); int utf8ncursor(struct utf8cursor *cursor, const struct utf8data *data, const char *s, size_t len);
The cursor structure must be provided by the caller, but is otherwise opaque; data is the database pointer obtained above. If the length of the string (in bytes) is known, utf8ncursor() should be used; utf8cursor() can be used when the length is not known but the string is null-terminated. These functions return zero on success, nonzero otherwise.
Working through the string is then accomplished by repeated calls to:
int utf8byte(struct utf8cursor *u8c);
This function will return the next byte in the normalized (and possibly case-folded) string, or zero at the end. UTF-8-encoded code points can take more than one byte, of course, so individual bytes do not, on their own, represent code points. Due to decomposition, the return string may be longer than the one passed in.
As an example of how these pieces fit together, here is the full implementation of utf8_strncasecmp():
int utf8_strncasecmp(const struct unicode_map *um, const struct qstr *s1, const struct qstr *s2) { const struct utf8data *data = utf8nfdicf(um->version); struct utf8cursor cur1, cur2; int c1, c2; if (utf8ncursor(&cur1, data, s1->name, s1->len) < 0) return -EINVAL; if (utf8ncursor(&cur2, data, s2->name, s2->len) < 0) return -EINVAL; do { c1 = utf8byte(&cur1); c2 = utf8byte(&cur2); if (c1 < 0 || c2 < 0) return -EINVAL; if (c1 != c2) return 1; } while (c1); return 0; }
There are other functions in the low-level API for testing validity, getting the length of strings, and so on, but the above captures the core of it. Those interested in the details can find them in this patch.
That is quite a bit of complexity when one considers that it is all there
just to compare strings; we are now far removed from the simple string
functions found in Kernighan & Ritchie. But that, it seems, is the
world that we live in now. At least we get some nice emoji for all of that
complexity 👍.
Index entries for this article | |
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Kernel | Character encoding |
Posted Mar 28, 2019 18:29 UTC (Thu)
by Sesse (subscriber, #53779)
[Link] (1 responses)
Posted Mar 29, 2019 9:32 UTC (Fri)
by grawity (subscriber, #80596)
[Link]
Posted Mar 28, 2019 21:48 UTC (Thu)
by ikm (guest, #493)
[Link] (55 responses)
Is case-insensitive file name support the only user of this code? Then being able to handle Unicode is hardly the requirement of the world we live in - we can already have emojis in file names, after all, and I doubt those are case sensitive.
Posted Mar 28, 2019 23:35 UTC (Thu)
by gdt (subscriber, #6284)
[Link] (7 responses)
Posted Mar 29, 2019 3:08 UTC (Fri)
by zlynx (guest, #2285)
[Link] (5 responses)
Always assume someone stole your filename. It isn't your until you hold a handle to it.
So how is this case normalization system helping anyone?
Posted Mar 29, 2019 6:09 UTC (Fri)
by khim (subscriber, #9252)
[Link] (4 responses)
P.S. I wonder if these tables (without code) could be exposed to userspace. Userspace guys ALSO often need to deal with Unicode and if kernel already has all these tables... why not use them?
Posted Mar 29, 2019 6:35 UTC (Fri)
by Cyberax (✭ supporter ✭, #52523)
[Link] (3 responses)
Posted Mar 29, 2019 8:26 UTC (Fri)
by felix.s (guest, #104710)
[Link] (2 responses)
Posted Mar 29, 2019 8:28 UTC (Fri)
by Cyberax (✭ supporter ✭, #52523)
[Link] (1 responses)
Posted Mar 29, 2019 9:31 UTC (Fri)
by dezgeg (subscriber, #92243)
[Link]
"The UTF-8 patches incorporate these rules by processing the provided files into a data structure in a C header file. A fair amount of space is then regained by removing the information for decomposing Hangul (Korean) code points into their base components, since this is a task that can be done algorithmically as well."
Exporting these non-standard tables to userspace would lock in this custom format implementation detail forever.
Posted Apr 1, 2019 14:12 UTC (Mon)
by rweikusat2 (subscriber, #117920)
[Link]
Such a lock must already exists, BTW, it may be sufficient to expose that. Advisory locking would probably be ok as UNIX processes are usually supposed to cooperate and not fight with each other. Vastly simpler in the kernel than 'hard-coding' a specific, known-to-be-broken/ deficient case translation mechanism into certain filesystems. Considering cases like "vertical bar plus combining overline' (aka T, not going happen as that's an ASCII codepoint), I consider "kernel supports UTF-8" much more 'scary'.
Posted Mar 29, 2019 10:05 UTC (Fri)
by smurf (subscriber, #17840)
[Link] (46 responses)
There's another problem here. Correct case folding is locale dependent. One example: Turkish has an i and an ı (i without the dot). Unicode helpfully has an İ (capital I with a dot) right next to it. Guess what happens when you case-fold these in Turkey vs. everywhere else.
Posted Mar 29, 2019 11:21 UTC (Fri)
by Sesse (subscriber, #53779)
[Link] (40 responses)
Also, I don't think you can blame Unicode for the fact that Turkish and English has different alphabets.
Posted Mar 29, 2019 13:32 UTC (Fri)
by drag (guest, #31333)
[Link] (37 responses)
What it does mean is that your case insensitive lookups for the file system are actually case sensitive with insensitive elements. How sensitive it ends up being depends on what language a user uses.
Unless, of course, the kernel is aware of the user's locale and changes the responses accordingly.
Posted Mar 29, 2019 22:53 UTC (Fri)
by mirabilos (subscriber, #84359)
[Link] (36 responses)
Posted Mar 30, 2019 13:17 UTC (Sat)
by SLi (subscriber, #53131)
[Link] (6 responses)
Posted Apr 4, 2019 8:33 UTC (Thu)
by dvdeug (guest, #10998)
[Link] (5 responses)
Posted Apr 5, 2019 8:11 UTC (Fri)
by dgm (subscriber, #49227)
[Link] (4 responses)
So Linux cannot exchange data with MacOS and Windows?! PANIC!
Or put another way: if I show you that less than 1% of the population really wants or needs a case-insensitive filesystem, can I disregard your claims?
Posted Apr 8, 2019 2:02 UTC (Mon)
by dvdeug (guest, #10998)
[Link] (3 responses)
Posted Apr 8, 2019 21:18 UTC (Mon)
by foom (subscriber, #14868)
[Link] (2 responses)
That may be, but FAT, exFAT, and NTFS don't use the unicode case folding rules. If the justification is to make something compatible with those systems, do we actually need the (rather complex) unicode rules?
Posted Apr 8, 2019 23:30 UTC (Mon)
by dvdeug (guest, #10998)
[Link] (1 responses)
In what way are the Unicode case-folding rules rather complex? They are for the most part fairly simple, one to one matchings of characters, with a few exceptions that you just have to deal with. The German ß and the various titlecase characters in Unicode are there and are going to have to be dealt with.
Posted Apr 9, 2019 15:35 UTC (Tue)
by foom (subscriber, #14868)
[Link]
You say that other cases "have to be dealt with"...but we have widely used examples showing that to not actually be the case.
Posted Mar 30, 2019 13:59 UTC (Sat)
by SLi (subscriber, #53131)
[Link] (28 responses)
Posted Mar 30, 2019 16:45 UTC (Sat)
by foom (subscriber, #14868)
[Link] (27 responses)
Neither Mac nor windows filesystems' case folding is locale sensitive, either. (NTFS does write a file during filesystem creation containing the case folding rules for that drive, so you _could_ make them be whatever you like, at the risk of breaking everything...)
Everyone likes to bring up this example, but I rather expect the likelihood of normal Turkish users noticing and caring that they can't create two such files in the same directory is rather a theoretical problem, not an actual one.
Posted Mar 30, 2019 18:19 UTC (Sat)
by nybble41 (subscriber, #55106)
[Link] (4 responses)
Posted Mar 30, 2019 21:41 UTC (Sat)
by mirabilos (subscriber, #84359)
[Link] (3 responses)
So, the kernel should have nothing to do with this *at all*.
Posted Apr 1, 2019 9:45 UTC (Mon)
by nim-nim (subscriber, #34454)
[Link] (2 responses)
Posted Apr 5, 2019 1:24 UTC (Fri)
by xtifr (guest, #143)
[Link] (1 responses)
This means *all* the overheads will truly need to be present only for those who actively *use* the system.
I honestly don't know how this is all going forward without *at least* a user-space proof-of-concept system.
Posted Apr 6, 2019 21:56 UTC (Sat)
by foom (subscriber, #14868)
[Link]
But that behavior would be pretty awful -- which files you can access depending upon your current locale? There's a reason filesystems (including this ext4 proposal) store the mapping used when creating the filesystem...
> without *at least* a user-space proof-of-concept system.
Two have been mentioned already. Android has an overlay filesystem for local access, and samba implements it when exporting the filesystem over the network.
Posted Mar 30, 2019 21:44 UTC (Sat)
by mirabilos (subscriber, #84359)
[Link] (6 responses)
Another reason why this belongs into userspace.
And no, the turkish case is not theoretical. They have words which only differ in the dot above the i, and in one case, one of the two words is normal and one a rather crass insult, which led to (IIRC) a knife attack (well, some kind of real-life attack at the person) because they had no dotless i on their keyboard when texting.
I’ll quote someone else: just because your latin alphabet has 26 letters, not everyone else’s does. Imagine if we’d *always* (independent on what word it’s in) make “oo” compare the same as “u”, for example.
Posted Mar 30, 2019 21:51 UTC (Sat)
by Cyberax (✭ supporter ✭, #52523)
[Link] (1 responses)
Although I personally wouldn't blame the cellphone here.
Posted Mar 30, 2019 22:43 UTC (Sat)
by mpr22 (subscriber, #60784)
[Link]
Bad technology made it worse.
The cellphone doesn't get off scot-free here.
Posted Mar 31, 2019 1:46 UTC (Sun)
by foom (subscriber, #14868)
[Link] (3 responses)
Re: Turkish swears -- you can name your files either word just fine -- the filesystem does not be change your chosen filename to the other name! Only if you try to make files named both, in the same directory, will you run into an issue. I still claim that is *highly* unlikely.
If we treated oo and u as the same for filename comparison purposes, because that was a very common language's policy, I rather suspect that also wouldn't be a huge problem. (It'd be weird to have such behavior, as that isn't a common policy, however.)
Posted Mar 31, 2019 19:17 UTC (Sun)
by naptastic (guest, #60139)
[Link]
Which one‽ I've never heard of this and I am dying to know! MY BRAIN IS HUNGRY
Posted Apr 4, 2019 5:37 UTC (Thu)
by rgmoore (✭ supporter ✭, #75)
[Link]
This seems like the key to me. If the case folding rules can change, there's no way to guarantee that the same file will always be accessible the same way, and that's true whether the case folding happens in the kernel or in userspace.
Posted Apr 4, 2019 12:28 UTC (Thu)
by bosyber (guest, #84963)
[Link]
Posted Apr 1, 2019 6:46 UTC (Mon)
by marcH (subscriber, #57642)
[Link] (14 responses)
Check the numerous, real-world examples and references given in the comment to the previous LWN article: https://lwn.net/Articles/784041/ It's not just Turkish: like another natural language topic case-sensitivity is very complex and (among others) locale-specific - not just in theory but in practice.
foom wrote:
Interesting, references?
nybble41 wrote:
Wait... should Linux be "bug for bug" compatible or linguistically correct?
Posted Apr 3, 2019 2:51 UTC (Wed)
by dvdeug (guest, #10998)
[Link] (8 responses)
Posted Apr 3, 2019 5:07 UTC (Wed)
by marcH (subscriber, #57642)
[Link] (7 responses)
Posted Apr 3, 2019 6:18 UTC (Wed)
by dvdeug (guest, #10998)
[Link] (6 responses)
Posted Apr 8, 2019 17:53 UTC (Mon)
by hkario (subscriber, #94864)
[Link] (5 responses)
Posted Apr 8, 2019 20:30 UTC (Mon)
by dvdeug (guest, #10998)
[Link] (4 responses)
Posted Apr 9, 2019 18:30 UTC (Tue)
by mirabilos (subscriber, #84359)
[Link] (3 responses)
Posted Apr 10, 2019 0:50 UTC (Wed)
by dvdeug (guest, #10998)
[Link] (2 responses)
Posted Apr 17, 2019 22:15 UTC (Wed)
by chithanh (guest, #52801)
[Link]
ß (U+00DF) indeed has no uppercase mapping in Unicode.
So if you start with ẞ and then convert to lowercase and then to uppercase again you might end up with SS.
Also, if you perform a case-insensitive filename match for ẞ it will return a file named ß.
Posted Apr 17, 2019 22:40 UTC (Wed)
by marcH (subscriber, #57642)
[Link]
Just for fun, some more "real-world" case insensitivity (from comments in the previous LWN thread)
Good luck supporting this in your filesystem.
> If the German speakers really wanted a change,...
Thanks, you just confirmed case sensitivity is not "hard science" no matter how hard Unicode tries to pretend it is. What a surprise considering it's part of natural languages. That's why it definitely has a place in high level interface user interfaces like file explorers, choosers and maybe interactive command lines even (with some autocorrection) but certainly not "hardwired" at a very low level in filesystems where it has already been seen causing damage.
Posted Apr 4, 2019 13:00 UTC (Thu)
by foom (subscriber, #14868)
[Link] (4 responses)
Search for $upcase -- the name of the 128KB pseudo file stored on in every NTFS filesystem. You can also look at the NTFS filesystem driver for Linux.
This file contains the corresponding uppercased character (2 bytes) for each one of the 65536 unicode characters. When windows wants to compare filenames, it simply indexes each character in each string through this table, to make an uppercase string, before doing the comparison.
When you reformat a drive it writes the newest mapping to the file, and that partition will use the same mapping as long as you keep it.
And, yes, I am quite aware that everyone who knows anything about unicode is crying out in distress at the utter WRONGness of what I said above...
But of course, the secret is that users aren't really the ones who care about case insensitive comparisons... They are using gui file pickers and such higher level tools where the filesystem case behavior doesn't matter.
Note the primary use cases given for Linux (samba exports, Android emulating a FAT filesystem on top of ext4) are all about *software* expectations, not humans. Software that was written with hardcoded filenames of the wrong case. That's why ntfs's braindead case folding is not really a problem.
Which does rather bring into question whether implementing "correct" normalization and case folding in Linux even has a point... It won't make it more compatible with the legacy software to do that...
Posted Apr 8, 2019 6:21 UTC (Mon)
by cpitrat (subscriber, #116459)
[Link] (3 responses)
Posted Apr 8, 2019 21:49 UTC (Mon)
by foom (subscriber, #14868)
[Link]
It does seem rather incongruous to me to justify the feature via by pointing to samba's emulation of NTFS case folding, and Android's emulation of FAT file name lookup rules, but then implementing unicode normalization and correct unicode case folding...which those don't do.
Posted Apr 11, 2019 20:49 UTC (Thu)
by Wol (subscriber, #4433)
[Link] (1 responses)
Forcing all filenames to be valid utf-16 will break quite a lot elsewhere ... I think that if you want to implement the utf universe properly in utf-16, you end up back with the 8-bit codeset mess, only bigger ...
Cheers,
Posted Apr 11, 2019 23:15 UTC (Thu)
by foom (subscriber, #14868)
[Link]
It stores filenames as arbitrary sequences of 16-bit values. There are a few tens of values you cannot use (ascii control characters 0-31, and some ascii punctuation), but everything else is fair game. In particular, invalid utf16 containing broken surrogate pairs is perfectly fine.
Posted Apr 7, 2019 22:40 UTC (Sun)
by jschrod (subscriber, #1646)
[Link]
I think a case could be made that one could blame Unicode for *not* representing these different alphabets. After all, the same code point is used for "different" characters in the alphabets - if one agrees to your statement that these are really different alphabets.
But, in real life, too much water has flown under this bridge to discuss it outside an evening in a wine bar with some friends who are encoding freaks. I have to admit I would be part of such a discussion... ;-)
Cheers, Joachim
Posted Apr 11, 2019 13:12 UTC (Thu)
by robbe (guest, #16131)
[Link]
Posted Mar 29, 2019 14:54 UTC (Fri)
by mina86 (guest, #68442)
[Link] (4 responses)
Posted Mar 30, 2019 4:27 UTC (Sat)
by gps (subscriber, #45638)
[Link] (1 responses)
What's one more? Some of the above could even go away after this in some system designs.
Posted Mar 31, 2019 14:41 UTC (Sun)
by mina86 (guest, #68442)
[Link]
That may be so but I'd rather my Samba server crashed than my kernel oopsed or executed malicious code because Unicode was handled incorrectly. Just like putting HTTP server inside the kernel wasn't a good idea, I'm not yet convinced that putting Unicode handling is.
Posted Apr 8, 2019 6:24 UTC (Mon)
by cpitrat (subscriber, #116459)
[Link] (1 responses)
Posted Apr 11, 2019 20:57 UTC (Thu)
by Wol (subscriber, #4433)
[Link]
Cheers,
Posted Apr 2, 2019 21:10 UTC (Tue)
by daniels (subscriber, #16193)
[Link] (2 responses)
Posted Apr 2, 2019 23:31 UTC (Tue)
by nix (subscriber, #2304)
[Link] (1 responses)
Posted Apr 11, 2019 5:01 UTC (Thu)
by lysse (guest, #3190)
[Link]
Posted Apr 12, 2019 20:12 UTC (Fri)
by donbarry (guest, #10485)
[Link]
At this rate, and aided by its UTF library, by Zawinski's law soon the kernel will contain an email client.
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
This is the story: https://gizmodo.com/a-cellphones-missing-dot-kills-two-pe...
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Hopefully the filesystem records what mapping it was created with, like NTFS does. Otherwise, some of your files may become inaccessible when a new mapping is switched to (which, iirc, did happen on HFS+ before. That's not good...)
Working with UTF-8 in the kernel
Is it? I know that it might be that way effectively in German, but in Dutch it is absolutely not, they are completely different sounds (the german u sound is closer to Dutch oe double sound, but not oo which is a loong vowel in Dutch.).
Working with UTF-8 in the kernel
> Neither Mac nor windows filesystems' case folding is locale sensitive, either. (NTFS does write a file during filesystem creation containing the case folding rules for that drive, so you _could_ make them be whatever you like, at the risk of breaking everything...)
> The fact that case folding is broken everywhere else it's been implemented offers a good argument against implementing it in Linux.
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
But ẞ (U+1E9E) has a lowercase mapping of ß.
But a case-insensitive filename match for ß will not return a file named ẞ.
Working with UTF-8 in the kernel
a file named ß.
> But a case-insensitive filename match for ß will not return a file named ẞ.
https://www.google.com/search?q=FRANCAIS
https://www.google.com/search?q=FRANÇAIS
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Wol
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Wol
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel
Working with UTF-8 in the kernel