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QFileSystemEngine::cloneFile: expand the Linux cloning process

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FICLONE only works on (currently) btrfs and xfs, and then only if it's
the same mount, so it's of very limited use. There are a couple other
techniques we may try that do not involve I/O through user-space, though
not immediate:
 - sendfile(2) can be used on regular files, even across mountpoints
 - sendfile(2) can be used on block devices too, but we need to get the
   device's size first
 - splice(2) can be used on pipes (FIFOs)

We only implement the first technique (earlier iterations of this patch
implemented all).

Change-Id: I81480fdb578d4d43b3fcfffd14d4b47cd70495a3
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
This commit is contained in:
Thiago Macieira 2017-07-25 15:50:24 -07:00 committed by Simon Hausmann
parent 974b3adf8a
commit 9c112a37ba
1 changed files with 42 additions and 3 deletions
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45
src/corelib/io/qfilesystemengine_unix.cpp
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@ -1084,13 +1084,52 @@ bool QFileSystemEngine::cloneFile(int srcfd, int dstfd, const QFileSystemMetaDat
} else if (knownData.hasFlags(QFileSystemMetaData::PosixStatFlags) &&
knownData.isDirectory()) {
return false; // fcopyfile(3) returns success on directories
} else if (QT_FSTAT(srcfd, &statBuffer) == -1 || S_ISDIR(statBuffer.st_mode)) {
} else if (QT_FSTAT(srcfd, &statBuffer) == -1) {
return false;
} else if (!S_ISREG((statBuffer.st_mode))) {
// not a regular file, let QFile do the copy
return false;
}
#if defined(Q_OS_LINUX)
// try FICLONE (only works on regular files and only on certain fs)
return ::ioctl(dstfd, FICLONE, srcfd) == 0;
if (statBuffer.st_size == 0) {
// empty file? we're done.
return true;
}
// first, try FICLONE (only works on regular files and only on certain fs)
if (::ioctl(dstfd, FICLONE, srcfd) == 0)
return true;
// Second, try sendfile (it can send to some special types too).
// sendfile(2) is limited in the kernel to 2G - 4k
auto sendfileSize = [](QT_OFF_T size) { return size_t(qMin<qint64>(0x7ffff000, size)); };
ssize_t n = ::sendfile(dstfd, srcfd, NULL, sendfileSize(statBuffer.st_size));
if (n == -1) {
// if we got an error here, give up and try at an upper layer
return false;
}
statBuffer.st_size -= n;
while (statBuffer.st_size) {
n = ::sendfile(dstfd, srcfd, NULL, sendfileSize(statBuffer.st_size));
if (n == 0) {
// uh oh, this is probably a real error (like ENOSPC), but we have
// no way to notify QFile of partial success, so just erase any work
// done (hopefully we won't get any errors, because there's nothing
// we can do about them)
n = ftruncate(dstfd, 0);
n = lseek(srcfd, 0, SEEK_SET);
n = lseek(dstfd, 0, SEEK_SET);
return false;
}
if (n == 0)
return true;
statBuffer.st_size -= n;
}
return true;
#elif defined(Q_OS_DARWIN)
// try fcopyfile
return fcopyfile(srcfd, dstfd, nullptr, COPYFILE_DATA | COPYFILE_STAT) == 0;