fs: use `ftruncate` in `AllocateFileRange` on OpenBSD #32645

pull theStack wants to merge 1 commits into bitcoin:master from theStack:202505-fs-use_ftruncate_on_openbsd changing 1 files +4 −1

theStack commented at 1:41 PM on May 30, 2025: contributor

Closes #32643.

Tested on OpenBSD 7.7 (amd64) by running a signet IBD, with the following patch on top to ensure the fallback isn't executed anymore:

diff --git a/src/util/fs_helpers.cpp b/src/util/fs_helpers.cpp
index 84ac3690c9..c6dff2d29d 100644
--- a/src/util/fs_helpers.cpp
+++ b/src/util/fs_helpers.cpp
@@ -208,6 +208,7 @@ void AllocateFileRange(FILE* file, unsigned int offset, unsigned int length)
     // OpenBSD doesn't have fallocate or posix_fallocate, use ftruncate
     if (0 == ftruncate(fileno(file), nEndPos)) return;
 #endif
+    assert(false);
     // Fallback version
     // TODO: just write one byte per block
     static const char buf[65536] = {};

Didn't run any performance tests, happy to take inputs on how to best measure any potential difference.

For another reference, here's an OpenBSD ports patch for kitty that replaces posix_fallocate with ftruncate: https://github.com/openbsd/ports/blob/master/x11/kitty/patches/patch-glfw_backend_utils_c

fs: use ftruncate in AllocateFileRange on OpenBSD
Closes issue #32643.
9982d525c5
DrahtBot commented at 1:41 PM on May 30, 2025: contributor


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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32645.



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Conflicts

Reviewers, this pull request conflicts with the following ones:
- #33228 (Bugfix: AllocateFileRange: Address various issues by luke-jr)
If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

in src/util/fs_helpers.cpp:201 in 9982d525c5

 199 | @@ -200,10 +200,13 @@ void AllocateFileRange(FILE* file, unsigned int offset, unsigned int length)
 200 |      }
 201 |      ftruncate(fileno(file), static_cast<off_t>(offset) + length);

luke-jr commented at 9:19 PM on June 6, 2025:

We're already calling fallocate here... seems like this whole #if mess should be sorted out.

in src/util/fs_helpers.cpp:207 in 9982d525c5

 199 | @@ -200,10 +200,13 @@ void AllocateFileRange(FILE* file, unsigned int offset, unsigned int length)
 200 |      }
 201 |      ftruncate(fileno(file), static_cast<off_t>(offset) + length);
 202 |  #else
 203 | +    off_t nEndPos = (off_t)offset + length;
 204 |  #if defined(HAVE_POSIX_FALLOCATE)
 205 |      // Version using posix_fallocate
 206 | -    off_t nEndPos = (off_t)offset + length;
 207 |      if (0 == posix_fallocate(fileno(file), 0, nEndPos)) return;
 208 | +#elif defined(__OpenBSD__)

luke-jr commented at 9:20 PM on June 6, 2025:

ftruncate isn't OpenBSD-specific. We should just check its availability and use it on platforms that support it (after preferred methods are ruled out)

luke-jr commented at 4:27 PM on June 30, 2025:

OTOH, ftruncate doesn't actually guarantee allocation... does OpenBSD provide such a guarantee?

luke-jr changes_requested
achow101 added the label Up for grabs on Oct 22, 2025
achow101 commented at 3:04 PM on October 22, 2025: member

Closing this as it has not had any activity in a while. If you are interested in continuing work on this, please leave a comment so that it can be reopened.

cc @davidgumberg @vasild
achow101 closed this on Oct 22, 2025

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#32643 fs: use `ftruncate` on OpenBSD in `AllocateFileRange`

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