init: fixes file descriptor accounting #30065
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We are computing our file descriptions limits based on whether we use poll or select. However, we are taking that into account only partially (subtracting from fd_max in one case, but from nFD later on). Moreover, nBind is also only accounted for partially. Simplify and fix this logic
The current logic for file descriptor accounting is pretty convoluted and hard to follow. This is partially caused by the lack of documentation plus non-intuitive variable naming (which was more intuitive when fewer things were accounted for, but hasn't aged well). This has led to this accounting being error-prone and hard to maintain (as shown in he previous commit). Redefine some of the constants, plus document what are we accounting for so this can be extended more easily
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src/init.cpp
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| nMaxConnections = std::max(std::min<int>(nMaxConnections, fd_max - nBind - MIN_CORE_FILEDESCRIPTORS - MAX_ADDNODE_CONNECTIONS - NUM_FDS_MESSAGE_CAPTURE), 0); | ||
| if (nFD < MIN_CORE_FILEDESCRIPTORS) | ||
| return InitError(_("Not enough file descriptors available.")); | ||
| nMaxConnections = std::min(nFD - MIN_CORE_FILEDESCRIPTORS - MAX_ADDNODE_CONNECTIONS - NUM_FDS_MESSAGE_CAPTURE, nMaxConnections); |
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Notice how the latter nMaxConnections trim is redundant once we limit nFD = std::min(FD_SETSIZE, nFD);. Moving things around, plus accounting for nBind (which is currently not being accounted for in master), we get:
nMaxConnections = std::max(std::min<int>(nMaxConnections, nFD - nBind - MIN_CORE_FILEDESCRIPTORS - MAX_ADDNODE_CONNECTIONS - NUM_FDS_MESSAGE_CAPTURE), 0);
nMaxConnections = std::min(nMaxConnections, nFD - nBind - MIN_CORE_FILEDESCRIPTORS - MAX_ADDNODE_CONNECTIONS - NUM_FDS_MESSAGE_CAPTURE,);
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Concept ACK |
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I think it is worth mentioning that the current approach is defining the minimum amount of file descriptions required without accounting for a single connection*, this means that if we are at the bare minimum, we will run but won't be able to connect to any nodes. This is consistent with the current logic in master, but I think it's not the way it should be. I'm happy to add another commit addressing this, but I've rathered start approaching this sticking to the same assumptions as master. * This actually accounts for manual connections, which may never happen, but not to any of our outbound. If we happen to not create any manuals we'd have 8 slots ( |
src/init.cpp
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| #endif | ||
| if (nFD < MIN_CORE_FDS) | ||
| return InitError(strprintf(_("Not enough file descriptors available. %d available, %d required."), nFD, MIN_CORE_FDS)); | ||
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| // Trim requested connection counts, to fit into system limitations | ||
| // <int> in std::min<int>(...) to work around FreeBSD compilation issue described in #2695 |
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I think now could also be the time to remove this FreeBSD workaround. It was needed because older versions of FreeBSD, used to ship with an old Clang (3.x). However we now require Clang 15+, and the effected version of FreeBSD 10.x, is long EOL.
Not relevant anymore. We require Clang 15+ (instead of Clang 3.x). Plus the affected version of FreeBSD 10.x, is long EOL.
The current logic for file descriptor accounting is pretty convoluted and hard to follow. This is partially caused by the lack of documentation plus non-intuitive variable naming (which was more intuitive when fewer things were accounted for, but
hasn't aged well). This has led to this accounting being error-prone and hard to maintain (as shown in the first commit of this PR).
Redefine some of the constants, plus document what are we accounting for so this can be extended more easily
Fixes #18911