parisc: Reduce SIGRTMIN from 37 to 32 to behave like other Linux architectures
This patch reduces the value of SIGRTMIN on PARISC from 37 to 32, thus increasing the number of available RT signals and bring it in sync with other Linux architectures. Historically we wanted to natively support HP-UX 32bit binaries with the PA-RISC Linux port. Because of that we carried the various available signals from HP-UX (e.g. SIGEMT and SIGLOST) and folded them in between the native Linux signals. Although this was the right decision at that time, this required us to increase SIGRTMIN to at least 37 which left us with 27 (64-37) RT signals. Those 27 RT signals haven't been a problem in the past, but with the upcoming importance of systemd we now got the problem that systemd alloctes (hardcoded) signals up to SIGRTMIN+29 which is beyond our NSIG of 64. Because of that we have not been able to use systemd on the PARISC Linux port yet. Of course we could ask the systemd developers to not use those hardcoded values, but this change is very unlikely, esp. with PA-RISC being a niche architecture. The other possibility would be to increase NSIG to e.g. 128, but this would mean to duplicate most of the existing Linux signal handling code into the parisc specific Linux kernel tree which would most likely introduce lots of new bugs beside the code duplication. The third option is to drop some HP-UX signals and shuffle some other signals around to bring SIGRTMIN to 32. This is of course an ABI change, but testing has shown that existing Linux installations are not visibly affected by this change - most likely because we move those signals around which are rarely used and move them to slots which haven't been used in Linux yet. In an existing installation I was able to exchange either the Linux kernel or glibc (or both) without affecting the boot process and installed applications. Dropping the HP-UX signals isn't an issue either, since support for HP-UX was basically dropped a few months back with Kernel 3.14 in commit f5a408d5 already, when we changed EWOULDBLOCK to be equal to EAGAIN. So, even if this is an ABI change, it's better to change it now and thus bring PARISC Linux in sync with other architectures to avoid other issues in the future. Signed-off-by: Helge Deller <deller@gmx.de> Cc: Carlos O'Donell <carlos@systemhalted.org> Cc: John David Anglin <dave.anglin@bell.net> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Aaro Koskinen <aaro.koskinen@iki.fi> Cc: PARISC Linux Kernel Mailinglist <linux-parisc@vger.kernel.org> Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
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