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Make `moveFile` more atomic 

Rather than directly copying the source to its dest, copy it first to a
temporary location, and eventually move that temporary.
That way, the move is at least atomic from the point-of-view of the destination
This commit is contained in:
Théophane Hufschmitt 2022-04-13 14:48:31 +02:00
parent 90f9680733
commit 1ba5b3e001
2 changed files with 61 additions and 56 deletions
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62
src/libutil/filesystem.cc
View File

@ -1,6 +1,7 @@
#include <sys/time.h>
#include <filesystem>
#include "finally.hh"
#include "util.hh"
#include "types.hh"
@ -8,6 +9,59 @@ namespace fs = std::filesystem;
namespace nix {
static Path tempName(Path tmpRoot, const Path & prefix, bool includePid,
int & counter)
{
tmpRoot = canonPath(tmpRoot.empty() ? getEnv("TMPDIR").value_or("/tmp") : tmpRoot, true);
if (includePid)
return (format("%1%/%2%-%3%-%4%") % tmpRoot % prefix % getpid() % counter++).str();
else
return (format("%1%/%2%-%3%") % tmpRoot % prefix % counter++).str();
}
Path createTempDir(const Path & tmpRoot, const Path & prefix,
bool includePid, bool useGlobalCounter, mode_t mode)
{
static int globalCounter = 0;
int localCounter = 0;
int & counter(useGlobalCounter ? globalCounter : localCounter);
while (1) {
checkInterrupt();
Path tmpDir = tempName(tmpRoot, prefix, includePid, counter);
if (mkdir(tmpDir.c_str(), mode) == 0) {
#if __FreeBSD__
/* Explicitly set the group of the directory. This is to
work around around problems caused by BSD's group
ownership semantics (directories inherit the group of
the parent). For instance, the group of /tmp on
FreeBSD is "wheel", so all directories created in /tmp
will be owned by "wheel"; but if the user is not in
"wheel", then "tar" will fail to unpack archives that
have the setgid bit set on directories. */
if (chown(tmpDir.c_str(), (uid_t) -1, getegid()) != 0)
throw SysError("setting group of directory '%1%'", tmpDir);
#endif
return tmpDir;
}
if (errno != EEXIST)
throw SysError("creating directory '%1%'", tmpDir);
}
}
std::pair<AutoCloseFD, Path> createTempFile(const Path & prefix)
{
Path tmpl(getEnv("TMPDIR").value_or("/tmp") + "/" + prefix + ".XXXXXX");
// Strictly speaking, this is UB, but who cares...
// FIXME: use O_TMPFILE.
AutoCloseFD fd(mkstemp((char *) tmpl.c_str()));
if (!fd)
throw SysError("creating temporary file '%s'", tmpl);
closeOnExec(fd.get());
return {std::move(fd), tmpl};
}
void createSymlink(const Path & target, const Path & link,
std::optional<time_t> mtime)
{
@ -101,10 +155,16 @@ void moveFile(const Path & oldName, const Path & newName)
} catch (fs::filesystem_error & e) {
auto oldPath = fs::path(oldName);
auto newPath = fs::path(newName);
// For the move to be as atomic as possible, copy to a temporary
// directory
fs::path temp = createTempDir(newPath.parent_path(), "rename-tmp");
Finally removeTemp = [&]() { fs::remove(temp); };
auto tempCopyTarget = temp / "copy-target";
if (e.code().value() == EXDEV) {
fs::remove(newPath);
warn("Can’t rename %s as %s, copying instead", oldName, newName);
copy(fs::directory_entry(oldPath), newPath, true);
copy(fs::directory_entry(oldPath), tempCopyTarget, true);
renameFile(tempCopyTarget, newPath);
}
}
}

55
src/libutil/util.cc
View File

@ -508,61 +508,6 @@ void deletePath(const Path & path, uint64_t & bytesFreed)
}
static Path tempName(Path tmpRoot, const Path & prefix, bool includePid,
int & counter)
{
tmpRoot = canonPath(tmpRoot.empty() ? getEnv("TMPDIR").value_or("/tmp") : tmpRoot, true);
if (includePid)
return (format("%1%/%2%-%3%-%4%") % tmpRoot % prefix % getpid() % counter++).str();
else
return (format("%1%/%2%-%3%") % tmpRoot % prefix % counter++).str();
}
Path createTempDir(const Path & tmpRoot, const Path & prefix,
bool includePid, bool useGlobalCounter, mode_t mode)
{
static int globalCounter = 0;
int localCounter = 0;
int & counter(useGlobalCounter ? globalCounter : localCounter);
while (1) {
checkInterrupt();
Path tmpDir = tempName(tmpRoot, prefix, includePid, counter);
if (mkdir(tmpDir.c_str(), mode) == 0) {
#if __FreeBSD__
/* Explicitly set the group of the directory. This is to
work around around problems caused by BSD's group
ownership semantics (directories inherit the group of
the parent). For instance, the group of /tmp on
FreeBSD is "wheel", so all directories created in /tmp
will be owned by "wheel"; but if the user is not in
"wheel", then "tar" will fail to unpack archives that
have the setgid bit set on directories. */
if (chown(tmpDir.c_str(), (uid_t) -1, getegid()) != 0)
throw SysError("setting group of directory '%1%'", tmpDir);
#endif
return tmpDir;
}
if (errno != EEXIST)
throw SysError("creating directory '%1%'", tmpDir);
}
}
std::pair<AutoCloseFD, Path> createTempFile(const Path & prefix)
{
Path tmpl(getEnv("TMPDIR").value_or("/tmp") + "/" + prefix + ".XXXXXX");
// Strictly speaking, this is UB, but who cares...
// FIXME: use O_TMPFILE.
AutoCloseFD fd(mkstemp((char *) tmpl.c_str()));
if (!fd)
throw SysError("creating temporary file '%s'", tmpl);
closeOnExec(fd.get());
return {std::move(fd), tmpl};
}
std::string getUserName()
{
auto pw = getpwuid(geteuid());