squashfs-tools-ng VS ccan

... except that that is also subtly broken.

It works if you write multiple UTF-8 code-units in one go, but breaks if you send them in several writes, or if you use the ANSI API (with the A suffix). Guess what the Windows implementation of stdio (printf and friends) does.

I already had some fun with this: https://github.com/AgentD/squashfs-tools-ng/issues/96#issuec...

And we didn't even discuss command line argument passing yet :-)

I tried to test it with the only other two languages I know besides English: German and Mandarin. Specifically also, because the later requires multi-byte characters to work. Getting this to work at all in a Windows terminal on an existing, German Windows 7 installation was an adventure on it's own.

Turns out, trying to write language agnostic command line applications on Windows is a PITA.

IIRC fanalyzer is a fairly recent addition to gcc. Has it become reasonable usable yet?

I recall getting a bit excited when I first read about it, but the results I got where rather bizarre (e.g. every single function that allocated memory and returned a pointer to it was labeled as leaking memory).

It did the fun exercise myself once to riffle through the gcc manpage, cobble together warning flags and massage them into autoconf[1][2].

There is a very handy m4 script in the util-linux source for testing supported warning flags[3].

[1] https://git.infradead.org/mtd-utils.git/blob/HEAD:/configure...

[2] https://github.com/AgentD/squashfs-tools-ng/blob/master/conf...

[3] https://github.com/karelzak/util-linux/blob/master/m4/compil...

> Honestly I think you could be a little more respectful of the project that inspired yours.

I do. I had a lot of great "Huh? That's clever!" moments while reverse engineering the format and formed a mental image of a clearly brilliant programmer who managed to squeeze the last bits out of some data structures using really clever tricks that I myself probably wouldn't have come up with. During that time I gained a lot of respect for the project and the author.

Also, please don't forget: the whole project is the filesystem, the tools are just a part of that. I care about this project, which is why I decided to start this effort in the first place. Which I explicitly did not advertise as a replacement, but an augmentation (see [2]).

> I'd be angry too ... Definitely understandable.

Yes, I agree! And I can understand why in the heat of the moment you might write something angry and threatening. But certainly not if you've had a few weeks time to calm down and think things over.

> And you plagiarized part of his readme.

https://github.com/plougher/squashfs-tools/blob/master/RELEA...

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

https://github.com/AgentD/squashfs-tools-ng/blob/master/READ...

Oh yes? Which part?

> ... calling it spaghetti code (which isn't immediately verifiable)

Here you go, have fun: https://github.com/plougher/squashfs-tools/blob/master/squas...

However, I cannot blame anyone here, I totally get how those things happen and have witnessed it myself in action:

You write a simple tool supporting a larger project. It's written by the seat of your pants without much planning, since it's not big and does one simple job. Then it gets used in production, eventually requirements change, other people pile on patches, but try to keep the diff small, so it's reviewable and it receives maybe a little less care than the actual project it supports. Nobody bothers to overhaul it or write documentation because, hey, it works, and any large changes might risk breaking things.

Even if nobody is to blame for it, the end result is still the same: an undocumented mess that is hard to wrap your head around if you aren't the original author, who is the only one with the bigger picture.

I tried for roughly a week to pull the code (there are some more files than this and some of the inter dependencies are nasty) apart into stacked utility libraries and a pure command line parsing front end, with the hopes to maybe get this upstream once it is done. I gave up and decided that at this point I understood enough about the format to start afresh and not touch what I believed to be an unmaintained mess.

FWIW there is an on various BSDs that contains "beXXtoh", "leXXtoh", "htobeXX", "htoleXX" where XX is a number of bits (16, 32, 64).

That header is also available on Linux, but glibc (and compatible libraries) put named it instead.

See: man 3 endian (https://linux.die.net/man/3/endian)

Of course it gets a bit hairier if the code is also supposed to run on other systems.

MacOS has OSSwapHostToLittleIntXX, OSSwapLittleToHostIntXX, OSSwapHostToBigIntXX and OSSwapBigToHostIntXX in .

I'm not sure if Windows has something similar, or if it even supports running on big endian machines (if you know, please tell).

My solution for achieving some portability currently entails cobbling together a "compat.h" header that defines macros for the MacOS functions and including the right headers. Something like this:

https://github.com/AgentD/squashfs-tools-ng/blob/master/incl...

This is usually my go-to-solution for working with low level on-disk or on-the-wire binary data structures that demand a specific endianness. In C I use "load/store" style functions that memcpy the data from a buffer into a struct instance and do the endian swapping. The copying is also necessary because the struct in the buffer may not have proper alignment.

In C++ code, all of this can of course be neatly stowed away in a special class with overloaded operators that transparently takes care of everything and "decays" into a single integer and exactly the above code after compilation, but is IMO somewhat cleaner to read and adds much needed type safety.

I once foolishly thought, I'll write a tar parser because, "how hard can it be" [1].

I simply tried to follow the tar(5) man page[2], and got a reference test set from another website posted previously on HN[3].

Along the way I discovered that NetBSD pax apparently cannot handle the PAX format[3] and my parser inadvertently uncovered that git-archive was doing the checksums wrong, but nobody noticed because other tar parsers were more lax about it[4].

As the article describes (as does the man page), tar is actually a really simple format, but there are just so many variants to choose from.

Turns out, if you strive for maximum compatibility, it's easiest to stick to what GNU tar does. If you think about it, IMO in many ways the GNU project ended up doing "embrace, extend, extinguish" with Unix.

[1] https://github.com/AgentD/squashfs-tools-ng/tree/master/lib/...

[2] https://www.freebsd.org/cgi/man.cgi?query=tar&sektion=5

[3] https://mgorny.pl/articles/portability-of-tar-features.html

[4] https://www.spinics.net/lists/git/msg363049.html

A while ago I did some simplistic SquashFS pack/unpack benchmarks[1][2]. I was primarily interested in looking at the behavior of my thread-pool based packer, but as a side effect I got a comparison of compressor speed & ratios over the various available compressors for my Debian test image.

I must say that LZ4 definitely stands out for both compression and uncompression speed, while still being able to cut the data size in half, making it probably quite suitable for life filesystems and network protocols. Particularly interesting was also comparing Zstd and LZ4[3], the former being substantially slower, but at the same time achieving a compression ratio somewhere between zlib and xz, while beating both in time (in my benchmark at least).

[1] https://github.com/AgentD/squashfs-tools-ng/blob/master/doc/...

[2] https://github.com/AgentD/squashfs-tools-ng/blob/master/doc/...

[3] https://github.com/AgentD/squashfs-tools-ng/blob/master/doc/...

Hilarious!

But I remember the first time I saw such a program which never freed anything: jitterbug, the simple bug tracker which ran as a CGI script.

It indeed allows a very simple style!

Meanwhile, use ccan/tal (https://github.com/rustyrussell/ccan/blob/master/ccan/tal/_i...) and be happy :)

There's CCAN, maintained by kernel hacker Rusty Russell: http://ccodearchive.net/

Please note that the above link has been claimed by squatters and isn’t the right link for CCAN anymore! The maintainer suggests [1] just using the GitHub repo [2] instead.

[1] https://lists.ozlabs.org/pipermail/ccan/2022-September/00141...

[2] https://github.com/rustyrussell/ccan/

This is a great learning exercise but not very useful because using void* creates practical problems that the compiler cant help you with. IMHO, for a nice vector in C look at https://github.com/rustyrussell/ccan/blob/master/ccan/darray/darray.h

For more advanced intrusive lists in C, I've found that ccan's tlist2 (https://github.com/rustyrussell/ccan/blob/master/ccan/tlist2...) provides a decent model here.

Compared to the linux kernel's intrusive lists, it also tracks the offset of the list_node within the structure contained by the list, which eliminates another class of problems. It does still have the "using the iterator after the for loop is over" issue discussed in this article, but it also already tracks the types as Linus proposed doing in the article to resolve the issue.

ccan library https://github.com/rustyrussell/ccan I think it is used also in the linux kernel(?)

ccan (analagous to cpan, but for C rather than Perl.)

You could use a discriminated union in your list node. You could use a void pointer in your list node, allocate space as needed and memcpy the date into this space, or don't allocate and store pointers to the original data. You could use an intrusive list, like this.

The fallacy in the article is that anyone should code these functions. There's plenty of public domain libraries that do this correctly.

https://github.com/rustyrussell/ccan/blob/master/ccan/endian...