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Use flock() instead of UUCP-style locking for serial devices #1770
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Original file line number | Diff line number | Diff line change |
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@@ -27,6 +27,7 @@ | |
#include <signal.h> | ||
#include <string.h> | ||
#include <sys/stat.h> | ||
#include <sys/file.h> | ||
#ifdef _WIN32 | ||
#define VC_EXTRALEAN | ||
#define WIN32_LEAN_AND_MEAN | ||
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@@ -57,7 +58,7 @@ using std::string; | |
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namespace { | ||
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string GetLockFile(const string &path) { | ||
string GetUUCPLockFile(const string &path) { | ||
const string base_name = ola::file::FilenameFromPath(path); | ||
return ola::file::JoinPaths(UUCP_LOCK_DIR, "LCK.." + base_name); | ||
} | ||
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@@ -106,7 +107,7 @@ bool ProcessExists(pid_t pid) { | |
#endif // _WIN32 | ||
} | ||
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bool RemoveLockFile(const string &lock_file) { | ||
bool RemoveUUCPLockFile(const string &lock_file) { | ||
if (unlink(lock_file.c_str())) { | ||
OLA_WARN << "Failed to remove UUCP lock file: " << lock_file; | ||
return false; | ||
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@@ -140,6 +141,44 @@ bool UIntToSpeedT(uint32_t value, speed_t *output) { | |
return false; | ||
} | ||
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bool OpenAndFlock(const std::string &path, int oflag, int *fd) { | ||
// First, check if the path exists, there's no point trying to open it if not | ||
if (!FileExists(path)) { | ||
OLA_INFO << "Device " << path << " doesn't exist."; | ||
return false; | ||
} | ||
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// Now try to open the serial device. | ||
if (!TryOpen(path, oflag, fd)) { | ||
OLA_DEBUG << "Failed to open device " << path; | ||
return false; | ||
} | ||
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#ifdef HAVE_FLOCK | ||
if (flock(*fd, LOCK_EX | LOCK_NB) == -1) { | ||
OLA_INFO << "Failed to flock() device " << path; | ||
close(*fd); | ||
return false; | ||
} | ||
#else // HAVE_FLOCK | ||
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close(*fd); | ||
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return false; | ||
#endif // HAVE_FLOCK | ||
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#if HAVE_SYS_IOCTL_H | ||
// As a final safety mechanism, use ioctl(TIOCEXCL) if available to prevent | ||
// further opens. | ||
if (ioctl(*fd, TIOCEXCL) == -1) { | ||
OLA_WARN << "TIOCEXCL " << path << " failed: " << strerror(errno); | ||
close(*fd); | ||
return false; | ||
} | ||
#endif // HAVE_SYS_IOCTL_H | ||
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OLA_INFO << "Locked " << path << " using flock()"; | ||
return true; | ||
} | ||
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bool AcquireUUCPLockAndOpen(const std::string &path, int oflag, int *fd) { | ||
// This is rather tricky since there is no real convention for LCK files. | ||
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@@ -154,7 +193,7 @@ bool AcquireUUCPLockAndOpen(const std::string &path, int oflag, int *fd) { | |
} | ||
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// Second, clean up a stale lockfile. | ||
const string lock_file = GetLockFile(path); | ||
const string lock_file = GetUUCPLockFile(path); | ||
OLA_DEBUG << "Checking for " << lock_file; | ||
pid_t locked_pid; | ||
if (!GetPidFromFile(lock_file, &locked_pid)) { | ||
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@@ -173,7 +212,7 @@ bool AcquireUUCPLockAndOpen(const std::string &path, int oflag, int *fd) { | |
} | ||
// There is a race between the read & the unlink here. I'm not convinced it | ||
// can be solved. | ||
if (!RemoveLockFile(lock_file)) { | ||
if (!RemoveUUCPLockFile(lock_file)) { | ||
OLA_INFO << "Device " << path << " was locked by PID " << locked_pid | ||
<< " which is no longer active, however failed to remove stale " | ||
<< "lock file"; | ||
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@@ -207,15 +246,15 @@ bool AcquireUUCPLockAndOpen(const std::string &path, int oflag, int *fd) { | |
close(lock_fd); | ||
if (r != pid_file_contents.size()) { | ||
OLA_WARN << "Failed to write complete LCK file: " << lock_file; | ||
RemoveLockFile(lock_file); | ||
RemoveUUCPLockFile(lock_file); | ||
return false; | ||
} | ||
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// Now try to open the serial device. | ||
if (!TryOpen(path, oflag, fd)) { | ||
OLA_DEBUG << "Failed to open device " << path << " despite having the " | ||
<< "lock file"; | ||
RemoveLockFile(lock_file); | ||
RemoveUUCPLockFile(lock_file); | ||
return false; | ||
} | ||
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@@ -225,7 +264,7 @@ bool AcquireUUCPLockAndOpen(const std::string &path, int oflag, int *fd) { | |
if (ioctl(*fd, TIOCEXCL) == -1) { | ||
OLA_WARN << "TIOCEXCL " << path << " failed: " << strerror(errno); | ||
close(*fd); | ||
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RemoveLockFile(lock_file); | ||
RemoveUUCPLockFile(lock_file); | ||
return false; | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Again we should return false. |
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} | ||
#endif // HAVE_SYS_IOCTL_H | ||
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@@ -234,7 +273,7 @@ bool AcquireUUCPLockAndOpen(const std::string &path, int oflag, int *fd) { | |
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void ReleaseUUCPLock(const std::string &path) { | ||
const string lock_file = GetLockFile(path); | ||
const string lock_file = GetUUCPLockFile(path); | ||
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pid_t locked_pid; | ||
if (!GetPidFromFile(lock_file, &locked_pid)) { | ||
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@@ -243,10 +282,26 @@ void ReleaseUUCPLock(const std::string &path) { | |
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pid_t our_pid = getpid(); | ||
if (our_pid == locked_pid) { | ||
if (RemoveLockFile(lock_file)) { | ||
if (RemoveUUCPLockFile(lock_file)) { | ||
OLA_INFO << "Released " << lock_file; | ||
} | ||
} | ||
} | ||
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bool AcquireLockAndOpenSerialPort(const std::string &path, int oflag, int *fd) { | ||
#ifdef UUCP_LOCKING | ||
return AcquireUUCPLockAndOpen(path, oflag, fd); | ||
#else | ||
return OpenAndFlock(path, oflag, fd); | ||
#endif | ||
} | ||
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void ReleaseSerialPortLock(const std::string &path) { | ||
#ifdef UUCP_LOCKING | ||
ReleaseUUCPLock(path); | ||
#endif // UUCP_LOCKING | ||
} | ||
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} // namespace io | ||
} // namespace ola |
Original file line number | Diff line number | Diff line change |
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@@ -67,6 +67,9 @@ bool UIntToSpeedT(uint32_t value, speed_t *output); | |
* @returns true if the open succeeded, false otherwise. | ||
* | ||
* This fails-fast, it we can't get the lock immediately, we'll return false. | ||
* | ||
* @deprecated Use AcquireLockAndOpenSerialPort() instead. | ||
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* @see ReleaseUUCPLock() | ||
*/ | ||
bool AcquireUUCPLockAndOpen(const std::string &path, int oflag, int *fd); | ||
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@@ -75,8 +78,41 @@ bool AcquireUUCPLockAndOpen(const std::string &path, int oflag, int *fd); | |
* @param path The path to unlock. | ||
* | ||
* The lock is only removed if the PID matches. | ||
* | ||
* @deprecated Use ReleaseSerialPortLock() instead. | ||
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* @see AcquireUUCPLockAndOpen() | ||
*/ | ||
void ReleaseUUCPLock(const std::string &path); | ||
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/** | ||
* @brief Try to open the path and obtain a lock to control access | ||
* @param path the path to open | ||
* @param oflag flags passed to open | ||
* @param[out] fd a pointer to the fd which is returned. | ||
* @returns true if the open succeeded, false otherwise. | ||
* | ||
* Depending on the compile-time configuration, this will use either flock() | ||
* (the default) or UUCP locking. See: ./configure --enable-uucp-locking. | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Isn't this now doing both/all? |
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* | ||
* This fails-fast, it we can't get the lock immediately, we'll return false. | ||
* | ||
* @see ReleaseSerialPortLock() | ||
*/ | ||
bool AcquireLockAndOpenSerialPort(const std::string &path, int oflag, int *fd); | ||
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/** | ||
* @brief Release a lock for the serial port | ||
* @param path The path to unlock. | ||
* | ||
* If UUCP locking was used (see AcquireLockAndOpenSerialPort), the lockfile | ||
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* will be removed (but only if the PID matches). | ||
* | ||
* Does nothing if flock() was used (see ./configure --enable-uucp-locking). | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Again can't this do all/more now? |
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* | ||
* @see AcquireLockAndOpenSerialPort() | ||
*/ | ||
void ReleaseSerialPortLock(const std::string &path); | ||
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} // namespace io | ||
} // namespace ola | ||
#endif // INCLUDE_OLA_IO_SERIAL_H_ |
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Has sys/file.h existed forever, so we're not breaking UUCP builds which don't have it?
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I'm not sure, I'll investigate. However the header is checked by the configure script, and used without any #ifdefs in one other place (KarateLight).
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Ah okay, obviously that plugin breaking wouldn't have quite so much impact, but the plugin has been around for a while and no-one has complained so we're probably good...
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he flock call itself conforms to 4.4BSD, i.e. it's been around since 1997. So I think we're pretty safe here.
I could add guards around the #include (ifdef HAVE_SYS_FILE_H), but if it's worked so far then I don't see any reason to add the extra complexity. On inspection, I'm not actually sure why KarateLight includes this header at all.
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Yeah very good point about the fact it's worked!
I'm not sure about KarateLight either; @cpresser ?
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Unfortunately, I am not sure what to answer here. My C++ is quite rusty, I have not used it in years and sure have no idea which include contains which functionality.
I recall that I did include file locking of the serial-port-device in the karatelight code. A quick search turned up this piece of code here:
https://github.com/OpenLightingProject/ola/blob/master/plugins/karate/KarateLight.cpp#L121
Does that help?
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The
#include <sys/file.h>
has been there since the first version of KarateDevice.cpp (f69a26b), but theflock
call is in a different file (KarateLight.cpp). I suspect theflock
calls were originally in KarateDevice.cpp and got moved.It does mean, however, that there's not only the #include but also a real use of flock() in OLA already without any tests! Therefore we're probably pretty safe using it for all serial devices. Nevertheless, we'll keep the tests and the conditionals :)