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diff --git a/content/16/index.md b/content/16/index.md index 2cb12b3..a970d33 100644 --- a/content/16/index.md +++ b/content/16/index.md @@ -9,7 +9,7 @@ tags = ["experiments"] My main desktop PC tracks the latest LTS [release](https://kernel.org/) of the Linux kernel which very recently switched to the 5.15 line. Along with neat new features like the -[NTSF3 driver](https://lore.kernel.org/all/aa4aa155-b9b2-9099-b7a2-349d8d9d8fbd@paragon-software.com/) +[NTFS3 driver](https://lore.kernel.org/all/aa4aa155-b9b2-9099-b7a2-349d8d9d8fbd@paragon-software.com/) it also includes experimental support for [Link Time Optimization](https://llvm.org/docs/LinkTimeOptimization.html) through LLVM's diff --git a/content/17/index.md b/content/17/index.md index 2c79af6..f37ba18 100644 --- a/content/17/index.md +++ b/content/17/index.md @@ -3,7 +3,7 @@ date = 2022-02-13T18:25:11+01:00 title = "Getting MPD to parse TIT1 in MP3 files" [taxonomies] -tags = ["TIL"] +tags = ["bugs"] +++ I have a pretty extensive music library that I manage with MPD, the [Music diff --git a/content/19/index.md b/content/19/index.md new file mode 100644 index 0000000..792a6dd --- /dev/null +++ b/content/19/index.md @@ -0,0 +1,87 @@ ++++ +date = 2024-09-18T21:16:12+02:00 + +title = "KDE Plasma 6 and two bugs" + +[taxonomies] +tags = ["bugs"] + +[extra] +related = [] ++++ + +For the last couple of months I have been running [sway](https://swaywm.org/) on +my main desktop system after having been forced away from +[hikari](https://hub.darcs.net/raichoo/hikari) because of its practically halted +development and incompatibility with newer +[wlroots](https://gitlab.freedesktop.org/wlroots/wlroots/) versions. + +I never felt completely satisfied with it and the whole experience was rather +joyless, so about a week ago I decided to give [KDE Plasma +6](https://kde.org/announcements/megarelease/6/) a try after a surprisingly +decent experience on the [KDE Neon](https://neon.kde.org/) live image. + +Whilst undoubtedly greater in its complexity and code size than sway, to me +Plasma 6 seems like one of the last decent desktop environments still remaining. +It's incredibly customisable (but still comes with good defaults), looks nice +out of the box, and most importantly seems to care about providing a nicely +integrated and featureful experience. This even includes a companion app on +Android, [KDE Connect](https://kdeconnect.kde.org/). It remains to be seen +whether it will fully convince me in the long run, but for now I am very +satisfied with it. + +{{ img(path="kde-plasma.png", alt="A picture of the KDE Plasma 6 desktop +environment, with a browser window, a terminal, and an instance of Dolphin, a +file manager.", caption="KDE Plasma 6 with a few windows open") }} + +This last week was mostly spent learning about the desktop environment and +setting everything up exactly how I want it to be, but there were two notable +bugs to squash as well. + +The first one reared its ugly head once I enabled backwards-compatibility with +Qt5-based apps. I have a couple of such apps still, most prominently +[Mumble](https://www.mumble.info/) and [Quassel IRC](https://quassel-irc.org/). +Once the latter was built against the KFramework libraries, no more +notifications were shown... + +Fixing this ended up taking about two days, most of which were spent discovering +exactly how +[KNotifications](https://api.kde.org/frameworks/knotifications/html/index.html) +work. KDE provides apps with a tighter integration to the notification service, +allowing users to specify which types of notifications to show, and how. +Applications specify their notifications by shipping an `<app>.notifyrc` file. +KDE ties this file to the application by matching its base name to the name +given to the application (usually through a call to +`QCoreApplication::applicationName` or when creating +[KAboutData](https://api.kde.org/frameworks/kcoreaddons/html/classKAboutData.html)). + +It turns out that Quassel had recently been +[patched](https://github.com/quassel/quassel/commit/020c163421691fa37330826df92ac0a248721290) +to fix an issue where desktop environments did not show its icon correctly. This +required a call to `setDesktopFileName` in `KAboutData` to make environments +aware of the connection. However, Quassel's application name was +[changed in the same commit](https://github.com/quassel/quassel/commit/020c163421691fa37330826df92ac0a248721290#diff-c72daad7d2269a2ee21584002ef1f30f4415335358a6c6f7e7296d3290a51a91R117), +severing its link with the name given through its `quassel.notifyrc` file. This +seems to have been done in addition to the `setDesktopFileName` call and was not +necessary to solve the issue the commit was trying to address. + +I prepared a [pull request](https://github.com/quassel/quassel/pull/619) fixing +this issue by reverting part of the offending commit. + +{{ img(path="notification.png", width=412, format="png", alt="A picture of a +notification from Quassel IRC saying 'yay for notifications'.", caption="Glad to +have these back") }} + +The second bug I randomly came across whilst perusing `journalctl` and seeing +the following error from [Dolphin](https://apps.kde.org/dolphin/), KDE's file +manager: + + QString(View)::contains(): called on an invalid QRegularExpression object + (pattern is '\A(?:file:///home/wolf/[Z-A]/?)\z') + +Seeing this immediately made me wonder whether Dolphin plugs a URL straight into +a regular expression without escaping it, and the answer, of course, +[is yes](https://invent.kde.org/system/dolphin/-/blob/5c069471fccc41051b967be69f95655b3e0b73ef/src/dolphinviewcontainer.cpp#L554-557). +I spent most of today's afternoon hunting this issue down and preparing a [merge +request](https://invent.kde.org/system/dolphin/-/merge_requests/831) that fixes +it in an elegant way. diff --git a/content/19/kde-plasma.png b/content/19/kde-plasma.png Binary files differnew file mode 100644 index 0000000..7a7251d --- /dev/null +++ b/content/19/kde-plasma.png diff --git a/content/19/notification.png b/content/19/notification.png Binary files differnew file mode 100644 index 0000000..fbf11f6 --- /dev/null +++ b/content/19/notification.png diff --git a/content/20/index.md b/content/20/index.md new file mode 100644 index 0000000..fbc99c1 --- /dev/null +++ b/content/20/index.md @@ -0,0 +1,66 @@ ++++ +date = 2024-09-19T22:45:36+02:00 +title = "List mpv(1)'s watch_later entries with later(1)" + +[taxonomies] +tags = ["projects", "later(1)"] + +[extra] +related = [] ++++ + +If you are like me then you have a basically never-ending backlog of videos to +watch. Perhaps sometimes you even watch videos so long that they're basically +impossible to finish in one sitting. Or you have about an hour left on a video, +but you should really go to sleep. + +All of these require some way to remember the timestamp where you left off. I +use [`mpv(1)`](https://mpv.io/) to watch my videos and thankfully there is a +built-in way to do this. By default, hitting `Q` will quit the video and +remember the timestamp ([among other +settings](https://mpv.io/manual/stable/#resuming-playback)) for next time you +open the file. This works regardless of whether the video exists on your +filesystem or is streamed from a URL. + +After a while of using this you might amass more than a couple of unfinished +videos that `mpv(1)` knows about, but what it sadly does not provide is an easy +way to show you which videos those are... + +Whilst you can set +[`write-filename-in-watch-later-config`](https://mpv.io/manual/stable/#options-write-filename-in-watch-later-config) +and have `mpv(1)` save filenames and URLs in its watch later entries, quickly +finding them is another story. + +This is where a shared effort between my partner +[nortti](https://ahti.space/~nortti/) and me comes in: +[`later(1)`](https://git.oriole.systems/later/about/). It is a small Python +script that parses `mpv(1)`'s [watch +later](https://mpv.io/manual/stable/#watch-later) entries and displays them in a +human-readable and pretty manner: + +``` +albatross ~$ later +Sep 19 19:50 https://www.youtube.com/watch?v=VKGtMK4CGV4 # The 2 Hour Hunt for Light Arrows - OoT Randomizer +Sep 19 22:30 /home/wolf/Mall Grab - Understand feat. Brendan Yates.webm +``` + +From here it is easy to open up the video you want to continue watching: simply +paste the path or URL printed by `later(1)` into `mpv(1)`. + +You might notice that the YouTube video is commented with its title. This is not +information that `mpv(1)` saves, but `later(1)` can help here too. Using the +`-u` or `--update-titles` flag, it will extract video titles using +[`yt-dlp(1)`](https://github.com/yt-dlp/yt-dlp) and save them in its cache for +subsequent retrieval. This should work for any site that `yt-dlp(1)` itself +supports. + +If you have a Python available, setting up and using `later(1)` is trivial: +simply copy the script into a directory in your `$PATH` (and the manual into +`$MANPATH`) or use the `Makefile`: + +``` +$ PREFIX=~/.local make install +``` + +Do note that for `later(1)` to work correctly, the aforementioned +`write-filename-in-watch-later-config` setting needs to be set. diff --git a/content/21/index.md b/content/21/index.md new file mode 100644 index 0000000..384509f --- /dev/null +++ b/content/21/index.md @@ -0,0 +1,57 @@ ++++ +date = 2024-09-26T19:27:54+02:00 +title = "Pretty names for mount points in /etc/fstab" + +[taxonomies] +tags = ["TIL"] + +[extra] +related = [] ++++ + +The file manager I'm using on my Plasma 6 system, +[Dolphin](https://invent.kde.org/system/dolphin), has built-in support for +remote folders via the [KIO](https://invent.kde.org/frameworks/kio) framework. +Where before I was relying on [sshfs](https://github.com/libfuse/sshfs) mount +points in `/etc/fstab`, I decided to try out the Dolphin way and set up my +remote devices using its `sftp` backend. + +After a couple of days now I can say that this works beautifully... until you +want to access the remote device on something that does not interface with KIO. +This is especially important for me (and +[others](https://invent.kde.org/plasma/plasma-desktop/-/issues/71#note_640907)) +since I want to be able to browse networked filesystems via my terminal and have +the ability to directly open a terminal in that location through Dolphin, +something which is not possible with the KIO backend. + +So in the end I went back to mount points in `/etc/fstab`. One small problem +remained, however, and that was the way those mount points were displayed +within Dolphin. There seemed to be no way to customize a mount point's name or +icon, leading to an annoyingly long `/home/wolf/net/hosts/coleridge` entry in +the *Devices* section of Dolphin's places panel. + +I couldn't find any help in `fstab(5)`, and indeed I had never heard of a way +to give a mount point a "pretty name". However, after a bit of searching, I +found people offhandedly mentioning the `x-gvfs-name` option. Some more +searching revealed that nobody seems to care about documenting these features, +but I was finally able to find an authoritative source within [gvfs +itself](https://github.com/GNOME/gvfs/blob/989d746ed771fc5e5bf134677cf8d571170b262e/monitor/udisks2/what-is-shown.txt#L29-L35). + +Happily there's not only `x-gvfs-name` but also support for custom icons +through `x-gvfs-icon`. So, if you want your file manager to display a pretty +name and icon for one of your mount points, simply add the following to the +relevant entry in `/etc/fstab`: + +``` +x-gvfs-name=My%20Device,x-gvfs-icon=network-server +``` + +This should be possible at least on GNOME and KDE desktops. I imagine a bunch +of other environments and programs silently support this behaviour as well. + +{{ img(path="places.png", format="png", alt="A screenshot of Dolphin, KDE's +file manager, showing the user's home directory with the places panel on the +left side containing various categorized entries. The entries below the Devices +category read flood, demeter, coleridge, and OnePlus 12, each with its own +pretty name and relevant icon.", caption="Dolphin displaying pretty names and +icons in the *Devices* category") }} diff --git a/content/21/places.png b/content/21/places.png Binary files differnew file mode 100644 index 0000000..cfbd8e7 --- /dev/null +++ b/content/21/places.png diff --git a/content/22/index.md b/content/22/index.md new file mode 100644 index 0000000..c3ece23 --- /dev/null +++ b/content/22/index.md @@ -0,0 +1,52 @@ ++++ +date = 2024-09-28T18:23:12+02:00 +title = "MIME type subclassing and its consequences" + +[taxonomies] +tags = ["TIL"] + +[extra] +related = [] ++++ + +The freedesktop.org [shared MIME-info database +spec](https://specifications.freedesktop.org/shared-mime-info-spec/latest) says +the following in [section +2.11](https://specifications.freedesktop.org/shared-mime-info-spec/latest/ar01s02.html#subclassing): + +> A type is a subclass of another type if any instance of the first type is +> also an instance of the second. For example, all `image/svg+xml` files are +> also `application/xml`, `text/plain` and `application/octet-stream` files. +> Subclassing is about the format, rather than the category of the data (for +> example, there is no 'generic spreadsheet' class that all spreadsheets +> inherit from). +> +> Some subclass rules are implicit: +> - All `text/*` types are subclasses of `text/plain`. +> - All streamable types (ie, everything except the `inode/*` types) are subclasses of application/octet-stream. + +So far so good; this makes intuitive sense and seems sensible enough. There is +an interesting consequence of this rule when the MIME-info database is used by +desktop systems for file associations, however: **An application associated with +`application/octet-stream` will automatically be associated with all streamable +types as well.** + +This means that if you associate `application/octet-stream` with your text +editor, your desktop system will also suggest you open video and audio files +with that same text editor. This behaviour can be quite surprising, especially +if the association was added automatically when a file was opened through the +"Open with..." dialog. + +What is even more confusing if you don't happen to know the subclassing rule is +the fact that `~/.config/mimeapps.list` and applications interfacing with this +file will not even list the editor as associated with any audio or video files. +You might just skip over the entry it has for `application/octet-stream`, not +realizing its significance. Perhaps you even assume (understandably) that +`application/octet-stream` only specifies any file of "unknown" type. +User-facing documentation on desktop systems (if it even exists) does not +discuss this behaviour. + +Whilst looking into this I found an older KDE bug report with some [interesting +thoughts](https://bugs.kde.org/show_bug.cgi?id=425154#c2) on how to explain this +behaviour to the end user, but sadly as far as I have seen none of these have +made it into the system setting's file association dialog. diff --git a/content/23/index.md b/content/23/index.md new file mode 100644 index 0000000..442f383 --- /dev/null +++ b/content/23/index.md @@ -0,0 +1,140 @@ ++++ +date = 2024-10-02T18:42:07+02:00 +title = "musl and a curious Rust segfault" + +[taxonomies] +tags = ["bugs"] + +[extra] +related = [] ++++ + +About a week ago I noticed that [`fd(1)`](https://github.com/sharkdp/fd), a +Rust-based alternative to [`find(1)`](https://www.gnu.org/software/findutils/), +would suddenly segfault on my [musl](https://www.musl-libc.org/)-based server +system. Usually a segfault is nothing particularly special to my eyes, but this +one was different. Even just having `fd(1)` attempt to print its help text was +enough to trigger it, and when I attempted to debug it with +[`gdb(1)`](https://www.sourceware.org/gdb/), I saw the following: + +``` +(gdb) run +Starting program: /usr/bin/fd + +Program received signal SIGSEGV, Segmentation fault. +memcpy () at ../src_musl/src/string/x86_64/memcpy.s:18 +warning: 18 ../src_musl/src/string/x86_64/memcpy.s: No such file or directory +(gdb) bt +#0 memcpy () at ../src_musl/src/string/x86_64/memcpy.s:18 +#1 0x00007ffff7ab7177 in __copy_tls () at ../src_musl/src/env/__init_tls.c:66 +#2 0x00007ffff7ab730d in static_init_tls () at ../src_musl/src/env/__init_tls.c:149 +#3 0x00007ffff7aae89d in __init_libc () at ../src_musl/src/env/__libc_start_main.c:39 +#4 0x00007ffff7aae9c0 in __libc_start_main () at ../src_musl/src/env/__libc_start_main.c:80 +#5 0x00007ffff74107f6 in _start () +``` + +So... the segfault is in musl, not in `fd`!? + +I immediately checked whether other basic programs on the system worked. *They +did.* I checked when I last updated musl. *A couple of months ago, so that can't +be it.* I checked specifically whether another Rust-based program worked. *It +did.* + +`fd(1)` had been updated pretty recently, and I remembered it working correctly +about a month ago, so maybe something specific to `fd(1)`'s usage of Rust +triggered this segfault in musl? I wanted to make sure I could reproduce this in +a development environment, so I cloned the `fd(1)` repository, built a debug +release, and ran it... + +*It worked.* Huh!? + +I decided it was likely that [`portage`](https://wiki.gentoo.org/wiki/Portage), +Gentoo's package manager, was building the program differently, so I took care +to apply the same build flags to the development build. And what can I say: + +``` +error: failed to run custom build command for `crossbeam-utils v0.8.20` + +Caused by: + process didn't exit successfully: `fd/target/[...]/build-script-build` + (signal: 11, SIGSEGV: invalid memory reference) + +``` + +... it didn't even get to build the `fd` binary proper. A segfault again, too. +What on earth was going on? Why didn't this also happen in the `portage` build? + +Thankfully I now had a reproducer, so I did the only sensible thing and started +removing random build flags until I got `fd` to build again. This was our +culprit: + +``` +-Wl,-z,pack-relative-relocs +``` + +Already pretty out of my depth considering the fact that I couldn't fathom how +`fd(1)` got musl to segfault on `memcpy`, I now also found that a piece of the +puzzle required me to understand specific linker flags. *Oof.* + +Unsure what to do next I decided on a whim to compare the working and the +broken binary with `readelf(1)`. The most obvious difference was that the +working binary had its `.rela.dyn` +[relocation](https://en.wikipedia.org/wiki/Relocation_(computing)) section +populated with entries whilst the broken one was missing `.rela.dyn` but had +`.relr.dyn` instead. At a loss, I stopped and went to do something else. + +The story would probably have ended here had I not mentioned this conundrum to +[my partner](https://ahti.space/~nortti/) later in the day. We decided to have +another look at the binaries. After some discussion we determined that the +working binary was dynamically linked whilst the broken one wasn't. The other +working Rust-based program, [`rg(1)`](https://github.com/BurntSushi/ripgrep), +was also dynamically linked and had been built a while ago, so **at some point +`portage` must have stopped producing Rust executables that were dynamically +linked**. Finally some progress! + +At this point we need some background. Early on, Rust decided to use the +`x86_64-unknown-linux-musl` target to provide statically-linked binaries that +would run on a wide range of systems. Whilst support for dynamically linked +executables on musl systems was [added back in +2017](https://github.com/rust-lang/rust/pull/40113), the default behaviour was +never changed, so Gentoo has to make sure to disable static linking by passing +the `target-feature=-crt-static` flag. + +It does this in a system-wide fashion by setting an environment variable in +[`/etc/env.d`](https://wiki.gentoo.org/wiki//etc/env.d): + +``` +$ cat /etc/env.d/50rust-bin-1.80.1 +LDPATH="/usr/lib/rust/lib" +MANPATH="/usr/lib/rust/man" +CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_RUSTFLAGS="-C target-feature=-crt-static" +``` + +This setting should therefore be picked up by `portage` as well, but when I +examined its build environment it was simply not there. So finally we come to +the last piece of the puzzle: a [recent +change](https://gitweb.gentoo.org/repo/gentoo.git/commit/eclass/cargo.eclass?id=27d469a2114b4ad0b3e682854c50c806753eb472) +in how `RUSTFLAGS` are set within `portage`. Here's the important part: + +```bash +local -x CARGO_TARGET_"${TRIPLE}"_RUSTFLAGS="-C strip=none -C linker=${LD_A[0]}" +[[ ${#LD_A[@]} -gt 1 ]] && local CARGO_TARGET_"${TRIPLE}"_RUSTFLAGS+="$(printf -- ' -C link-arg=%s' "${LD_A[@]:1}")" +local CARGO_TARGET_"${TRIPLE}"_RUSTFLAGS+=" ${RUSTFLAGS}" +``` + +Quoth the `bash(1)` manual: + +> Local variables "shadow" variables with the same name declared at previous +> scopes. For instance, a local variable declared in a function hides a global +> variable of the same name: references and assignments refer to the local +> variable, leaving the global variable unmodified. + +When previously the `RUSTFLAGS` environment variable was only touched when +cross-compiling, it was now overridden. To confirm, I edited the file in +question to include the previous value, and both `fd(1)` and `rg(1)` worked +again. Success! + +This whole saga was also [reported](https://bugs.gentoo.org/940197) to the +Gentoo bug tracker and promptly fixed. A project for another day is figuring out +exactly how a change from static linking to dynamic linking causes segfaults +like this, because I sure would love to know the details. diff --git a/content/8/index.md b/content/8/index.md index 7bfcbb0..ac4b147 100644 --- a/content/8/index.md +++ b/content/8/index.md @@ -10,7 +10,7 @@ related = [9] +++ When maintaining a project sooner or later there comes the time when you need to -apply patches that have been submitted to you. Assuming a patch-based workflow +apply patches that have been submitted to you. Assuming a patch-based workflow, those are going to be one patch per mail, possibly connected in a thread. There's lots of different ways of getting those patches to their final destination, [`git-am(1)`](https://git-scm.com/docs/git-am), and in this post I |