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Refactor fstat into a wrapper in libutil #15111

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Merged
Ericson2314 merged 1 commit into from
Jan 28, 2026
Merged

Refactor fstat into a wrapper in libutil #15111

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5 changes: 2 additions & 3 deletions src/libstore/gc.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
#include "nix/util/signals.hh"
#include "nix/util/serialise.hh"
#include "nix/util/util.hh"
#include "nix/util/file-system.hh"
#include "nix/store/posix-fs-canonicalise.hh"

#include "store-config-private.hh"
Expand Down Expand Up @@ -68,9 +69,7 @@ void LocalStore::createTempRootsFile()

/* Check whether the garbage collector didn't get in our
way. */
PosixStat st;
if (fstat(fromDescriptorReadOnly(fdTempRoots->get()), &st) == -1)
throw SysError("statting '%1%'", fnTempRoots);
auto st = nix::fstat(fromDescriptorReadOnly(fdTempRoots->get()));
if (st.st_size == 0)
break;

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4 changes: 1 addition & 3 deletions src/libstore/unix/pathlocks.cc
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Expand Up @@ -111,9 +111,7 @@ bool PathLocks::lockPaths(const std::set<std::filesystem::path> & paths, const s

/* Check that the lock file hasn't become stale (i.e.,
hasn't been unlinked). */
PosixStat st;
if (fstat(fd.get(), &st) == -1)
throw SysError("statting lock file %1%", PathFmt(lockPath));
auto st = nix::fstat(fd.get());
if (st.st_size != 0)
/* This lock file has been unlinked, so we're holding
a lock on a deleted file. This means that other
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14 changes: 14 additions & 0 deletions src/libutil/file-system.cc
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Expand Up @@ -217,6 +217,20 @@ PosixStat lstat(const std::filesystem::path & path)
return st;
}

PosixStat fstat(int fd)
{
PosixStat st;
if (
#ifdef _WIN32
_fstat64
#else
::fstat
#endif
(fd, &st))
throw SysError("getting status of fd %d", fd);
return st;
}

std::optional<PosixStat> maybeStat(const std::filesystem::path & path)
{
std::optional<PosixStat> st{std::in_place};
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4 changes: 1 addition & 3 deletions src/libutil/fs-sink.cc
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Expand Up @@ -189,9 +189,7 @@ void RestoreRegularFile::isExecutable()
// Windows doesn't have a notion of executable file permissions we
// care about here, right?
#ifndef _WIN32
PosixStat st;
if (fstat(fd.get(), &st) == -1)
throw SysError("fstat");
auto st = nix::fstat(fd.get());
if (fchmod(fd.get(), st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
throw SysError("fchmod");
#endif
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4 changes: 4 additions & 0 deletions src/libutil/include/nix/util/file-system.hh
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Expand Up @@ -130,6 +130,10 @@ PosixStat lstat(const std::filesystem::path & path);
* Get status of `path` following symlinks.
*/
PosixStat stat(const std::filesystem::path & path);
/**
* Get status of an open file descriptor.
*/
PosixStat fstat(int fd);
/**
* `lstat` the given path if it exists.
* @return std::nullopt if the path doesn't exist, or an optional containing the result of `lstat` otherwise
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4 changes: 1 addition & 3 deletions src/libutil/posix-source-accessor.cc
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Expand Up @@ -55,9 +55,7 @@ void PosixSourceAccessor::readFile(const CanonPath & path, Sink & sink, std::fun
if (!fd)
throw SysError("opening file '%1%'", ap.string());

PosixStat st;
if (fstat(fromDescriptorReadOnly(fd.get()), &st) == -1)
throw SysError("statting file");
auto st = nix::fstat(fromDescriptorReadOnly(fd.get()));
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@xokdvium xokdvium Jan 28, 2026

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FWIW, fromDescriptorReadOnly performs a destructive move out of HANDLE on windows and that HANDLE must not be used anymore or closed with CloseHandle. Instead it must use a the ::close from the C runtime, so this is kind of borked. A pre-existing issue, but still something to keep in mind :(

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@Ericson2314 Ericson2314 Jan 28, 2026 •
edited
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Yes longer term we'll want to use https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfileinformationbyhandle


sizeCallback(st.st_size);

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5 changes: 1 addition & 4 deletions src/libutil/unix/file-descriptor.cc
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Expand Up @@ -51,10 +51,7 @@ void pollFD(int fd, int events)

std::string readFile(int fd)
{
PosixStat st;
if (fstat(fd, &st) == -1)
throw SysError("statting file");

auto st = nix::fstat(fd);
return drainFD(fd, true, st.st_size);
}

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