Build error on macOS: `notification.c: error: implicit declaration of function 'memfd_create' [-Wimplicit-function-declaration]`

[barracuda156]

[16/38] /opt/local/bin/gcc-mp-14 -Ilibportal/libportal.1.dylib.p -Ilibportal -I../libportal-0.9.1/libportal -I. -I../libportal-0.9.1 -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include/gio-unix-2.0 -I/opt/local/include -fvisibility=hidden -fdiagnostics-color=always -Wall -Winvalid-pch -Wextra -O0 -g -Wno-unused-parameter -Wno-missing-field-initializers -pipe -Os -arch ppc -MD -MQ libportal/libportal.1.dylib.p/notification.c.o -MF libportal/libportal.1.dylib.p/notification.c.o.d -o libportal/libportal.1.dylib.p/notification.c.o -c ../libportal-0.9.1/libportal/notification.c
FAILED: libportal/libportal.1.dylib.p/notification.c.o 
/opt/local/bin/gcc-mp-14 -Ilibportal/libportal.1.dylib.p -Ilibportal -I../libportal-0.9.1/libportal -I. -I../libportal-0.9.1 -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include/gio-unix-2.0 -I/opt/local/include -fvisibility=hidden -fdiagnostics-color=always -Wall -Winvalid-pch -Wextra -O0 -g -Wno-unused-parameter -Wno-missing-field-initializers -pipe -Os -arch ppc -MD -MQ libportal/libportal.1.dylib.p/notification.c.o -MF libportal/libportal.1.dylib.p/notification.c.o.d -o libportal/libportal.1.dylib.p/notification.c.o -c ../libportal-0.9.1/libportal/notification.c
../libportal-0.9.1/libportal/notification.c: In function 'bytes_to_memfd':
../libportal-0.9.1/libportal/notification.c:85:8: error: implicit declaration of function 'memfd_create' [-Wimplicit-function-declaration]
   85 |   fd = memfd_create (name, MFD_ALLOW_SEALING);
      |        ^~~~~~~~~~~~
../libportal-0.9.1/libportal/notification.c:85:28: error: 'MFD_ALLOW_SEALING' undeclared (first use in this function)
   85 |   fd = memfd_create (name, MFD_ALLOW_SEALING);
      |                            ^~~~~~~~~~~~~~~~~
../libportal-0.9.1/libportal/notification.c:85:28: note: each undeclared identifier is reported only once for each function it appears in
../libportal-0.9.1/libportal/notification.c: In function 'parse_media':
../libportal-0.9.1/libportal/notification.c:331:52: error: 'MFD_ALLOW_SEALING' undeclared (first use in this function)
  331 |           fd = memfd_create ("notification-media", MFD_ALLOW_SEALING);
      |                                                    ^~~~~~~~~~~~~~~~~

[smcv]

libportal is primarily designed to be used on Linux, which does have memfd. Is it useful to have it available on macOS?

It will not do anything useful unless https://github.com/flatpak/xdg-desktop-portal/ is available and working.

[barracuda156]

It is a required dependency for shotwell, which is why I started building it. I did not investigate standalone functionality, tbh.

[smcv]

If your platform doesn't have a working xdg-desktop-portal, then libportal isn't going to be any use to you, and making Shotwell only use libportal conditionally (if on Linux, or if available) is likely to be more useful than making libportal compile.

[barracuda156]

Flatpak as such seems to be a Linux thing, but FreeBSD’s FreshPorts still have libportal as a port and as a dependency for shotwell.
Generally speaking, some Linux stuff, while not commonly used on macOS, can be still sensible there and made to work. I do not know about this case, honestly.
If this app can potentially be useful on macOS, then it may still be useful to fix the code.

[smcv]

Flatpak is Linux-specific and intentionally non-portable, yes.

libportal isn't an app, it's a client library for xdg-desktop-portal. It can only be useful on platforms where x-d-p works (either "next to" the app, or on the other side of a container boundary). If x-d-p doesn't work, then libportal can't do anything useful: all API calls will just fail.

It looks as though the current version of x-d-p has a non-optional use of memfds for their security properties (the ability to "seal" a blob of memory so that it can be passed across AF_UNIX fd-passing without any process being able to alter it), and I'm not aware of a similar mechanism existing on other Unixes, so x-d-p is probably also Linux-specific at this point.

[Eveeifyeve]

To be fair, what are we supposed to use for Darwin GTK apps that require this since flatpak/libportal doesn't work on darwin? Since there will be a lot of apps broken on nixpkgs.

[smcv]

To be fair, what are we supposed to use for Darwin GTK apps that require this since flatpak/libportal doesn't work on darwin?

If libportal isn't useful on Darwin, please talk to the maintainers of apps that have chosen to depend on it. Either the app isn't portable beyond Linux as a result of the dependency, or the app could use libportal on Linux and do something different on other platforms, or the app could have reduced functionality on non-Linux platforms.

For example, Shotwell seems to use libportal to set the background or to send files via email. If the maintainers of Shotwell intend it to be portable to non-Linux platforms, then for each of those two features, it will need to either not offer the feature on non-Linux, or implement it some other way on non-Linux.

Since there will be a lot of apps broken on nixpkgs

I don't think you can expect there to be any guarantee that every app on nixpkgs is portable to Darwin. Some apps are not portable, and software distribution mechanisms that support multiple platforms need to be able to cope with the idea that not all of their apps are available on all platforms.

[smcv]

If the maintainers of Shotwell intend it to be portable to non-Linux platforms

Please note the "if" here: I do not know whether Shotwell is intended to be portable. It's entirely possible that the answer is either "no, it's Linux-specific", or "yes in principle, but only if a user of non-Linux platforms sends merge requests".

[LunNova]

It looks as though the current version of x-d-p has a non-optional use of memfds for their security properties (the ability to "seal" a blob of memory so that it can be passed across AF_UNIX fd-passing without any process being able to alter it), and I'm not aware of a similar mechanism existing on other Unixes, so x-d-p is probably also Linux-specific at this point.

FWIW FreeBSD has memfd_create and MFD_ALLOW_SEALING so it's not inherently limited to linux.