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QFileSystemEngine::fillMetaData: simplify and comment the code

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Took me a long while to understand what it did. Now that I do, I can
also answer the question left behind during the original implementation
in Qt 4.8 (commit 4fd2aced96d9095254d89f9da9c911bd88f15245 in the old
history): how to know if a file exists?

Change-Id: I8d96dea9955d4c749b99fffd14cdae135499a0d3
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Thiago Macieira 2017-07-02 18:34:09 -07:00
parent 12339481ea
commit 04f4d87bda
1 changed files with 65 additions and 38 deletions
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103
src/corelib/io/qfilesystemengine_unix.cpp
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@ -698,43 +698,62 @@ bool QFileSystemEngine::fillMetaData(const QFileSystemEntry &entry, QFileSystemM
}
#endif // defined(Q_OS_DARWIN)
// if we're asking for any of the stat(2) flags, then we're getting them all
if (what & QFileSystemMetaData::PosixStatFlags)
what |= QFileSystemMetaData::PosixStatFlags;
if (what & QFileSystemMetaData::ExistsAttribute) {
// FIXME: Would other queries being performed provide this bit?
what |= QFileSystemMetaData::PosixStatFlags;
}
data.entryFlags &= ~what;
const QByteArray nativeFilePath = entry.nativeFilePath();
bool entryExists = true; // innocent until proven otherwise
// first, we may try lstat(2). Possible outcomes:
// - success and is a symlink: filesystem entry exists, but we need stat(2)
// -> statBufferValid = false
// - success and is not a symlink: filesystem entry exists and we're done
// -> statBufferValid = true
// - failure: really non-existent filesystem entry
// -> entryExists = false; statBufferValid = true
// both stat(2) and lstat(2) may generate a number of different errno
// conditions, but of those, the only ones that could happen and the
// entry still exist are EACCES, EFAULT, ENOMEM and EOVERFLOW. If we get
// EACCES or ENOMEM, then we have no choice on how to proceed, so we may
// as well conclude it doesn't exist; EFAULT can't happen and EOVERFLOW
// shouldn't happen because we build in _LARGEFIE64.
QT_STATBUF statBuffer;
bool statBufferValid = false;
if (what & QFileSystemMetaData::LinkType) {
if (QT_LSTAT(nativeFilePath, &statBuffer) == 0) {
if (S_ISLNK(statBuffer.st_mode)) {
// it's a symlink, we don't know if the file "exists"
data.entryFlags |= QFileSystemMetaData::LinkType;
} else {
// it's a reagular file and it exists
statBufferValid = true;
data.entryFlags &= ~QFileSystemMetaData::PosixStatFlags;
data.fillFromStatBuf(statBuffer);
data.knownFlagsMask |= QFileSystemMetaData::PosixStatFlags
| QFileSystemMetaData::ExistsAttribute;
data.entryFlags |= QFileSystemMetaData::ExistsAttribute;
}
} else {
// it doesn't exist
entryExists = false;
data.knownFlagsMask |= QFileSystemMetaData::ExistsAttribute;
}
data.knownFlagsMask |= QFileSystemMetaData::LinkType;
}
// second, we try a regular stat(2)
if (statBufferValid || (what & QFileSystemMetaData::PosixStatFlags)) {
if (entryExists && !statBufferValid)
if (entryExists && !statBufferValid) {
statBufferValid = (QT_STAT(nativeFilePath, &statBuffer) == 0);
data.entryFlags &= ~QFileSystemMetaData::PosixStatFlags;
if (statBufferValid)
data.fillFromStatBuf(statBuffer);
}
if (statBufferValid)
data.fillFromStatBuf(statBuffer);
else {
if (!statBufferValid) {
entryExists = false;
data.birthTime_ = 0;
data.metadataChangeTime_ = 0;
@ -750,34 +769,49 @@ bool QFileSystemEngine::fillMetaData(const QFileSystemEntry &entry, QFileSystemM
| QFileSystemMetaData::ExistsAttribute;
}
// third, we try access(2)
if (what & (QFileSystemMetaData::UserPermissions | QFileSystemMetaData::ExistsAttribute)) {
// calculate user permissions
auto checkAccess = [&](QFileSystemMetaData::MetaDataFlag flag, int mode) {
if (!entryExists || (what & flag) == 0)
return;
if (QT_ACCESS(nativeFilePath, mode) == 0) {
// access ok (and file exists)
data.entryFlags |= flag | QFileSystemMetaData::ExistsAttribute;
} else if (errno != EACCES && errno != EROFS) {
entryExists = false;
}
};
checkAccess(QFileSystemMetaData::UserReadPermission, R_OK);
checkAccess(QFileSystemMetaData::UserWritePermission, W_OK);
checkAccess(QFileSystemMetaData::UserExecutePermission, X_OK);
// if we still haven't found out if the file exists, try F_OK
if (entryExists && (data.entryFlags & QFileSystemMetaData::ExistsAttribute) == 0) {
entryExists = QT_ACCESS(nativeFilePath, F_OK) == 0;
if (entryExists)
data.entryFlags |= QFileSystemMetaData::ExistsAttribute;
}
data.knownFlagsMask |= (what & QFileSystemMetaData::UserPermissions) |
QFileSystemMetaData::ExistsAttribute;
}
#if defined(Q_OS_DARWIN)
if (what & QFileSystemMetaData::AliasType)
{
if (what & QFileSystemMetaData::AliasType) {
if (entryExists && hasResourcePropertyFlag(data, entry, kCFURLIsAliasFileKey))
data.entryFlags |= QFileSystemMetaData::AliasType;
data.knownFlagsMask |= QFileSystemMetaData::AliasType;
}
#endif
if (what & QFileSystemMetaData::UserPermissions) {
// calculate user permissions
if (what & QFileSystemMetaData::BundleType) {
if (entryExists && isPackage(data, entry))
data.entryFlags |= QFileSystemMetaData::BundleType;
if (entryExists) {
if (what & QFileSystemMetaData::UserReadPermission) {
if (QT_ACCESS(nativeFilePath, R_OK) == 0)
data.entryFlags |= QFileSystemMetaData::UserReadPermission;
}
if (what & QFileSystemMetaData::UserWritePermission) {
if (QT_ACCESS(nativeFilePath, W_OK) == 0)
data.entryFlags |= QFileSystemMetaData::UserWritePermission;
}
if (what & QFileSystemMetaData::UserExecutePermission) {
if (QT_ACCESS(nativeFilePath, X_OK) == 0)
data.entryFlags |= QFileSystemMetaData::UserExecutePermission;
}
}
data.knownFlagsMask |= (what & QFileSystemMetaData::UserPermissions);
data.knownFlagsMask |= QFileSystemMetaData::BundleType;
}
#endif
if (what & QFileSystemMetaData::HiddenAttribute
&& !data.isHidden()) {
@ -791,15 +825,8 @@ bool QFileSystemEngine::fillMetaData(const QFileSystemEntry &entry, QFileSystemM
data.knownFlagsMask |= QFileSystemMetaData::HiddenAttribute;
}
#if defined(Q_OS_DARWIN)
if (what & QFileSystemMetaData::BundleType) {
if (entryExists && isPackage(data, entry))
data.entryFlags |= QFileSystemMetaData::BundleType;
data.knownFlagsMask |= QFileSystemMetaData::BundleType;
}
#endif
if (!entryExists) {
what &= ~QFileSystemMetaData::LinkType; // don't clear link: could be broken symlink
data.clearFlags(what);
return false;
}