On Tue, 29 Jul 2014 23:30:36 -0400 "Carlos O'Donell" <car...@redhat.com> wrote:
> On 07/23/2014 02:21 PM, Jeff Layton wrote: > > From: Jeff Layton <jlay...@poochiereds.net> > > Thanks for resending. Sorry for the delay. > > Your use of 3 different emails caused me to miss the recent > resends. That's my fault and tied to the way I'm tracking > everything from patchwork using the first email you used. > Sorry about that. I was hoping to get this wrapped up before changing jobs, but that obviously didn't happen... > I am assuming that this work is under Red Hat's copyright > status since you submitted it originally from @redhat.com. > Yeah, that should be fine. This work was all done under the aegis of Red Hat. The small tweaks you mention below are also OK. Thanks for getting this merged! > I've committed this to trunk with small tweaks and the following > NEWS entry: > > * Support for file description locks is added to systems running the > Linux kernel. The standard file locking interfaces are extended to > operate on file descriptions, not file descriptors, via the use of > F_OFD_GETLK, F_OFD_SETLK, and F_OFD_SETLKW. File description locks > are associated with an open file instead of a process. > > This will be in 2.20 when we cut the branch. > > > Open file description locks have been merged into the Linux kernel > > for v3.15. Add the appropriate command-value definitions and an > > update to the manual that describes their usage. > > > > ChangeLog: > > > > 2014-04-24 Jeff Layton <jlay...@poochiereds.net> > > > > [BZ#16839] > > * manual/llio.texi: add section about open file description > > locks > > > > * manual/examples/ofdlocks.c: > > example of open file description lock usage > > > > * sysdeps/unix/sysv/linux/bits/fcntl-linux.h: > > (F_OFD_GETLK, F_OFD_SETLK, F_OFD_SETLKW): New macros. > > I simplified it a bit. > > A space in the ChangeLog indicates a distinct commit, which this is > not, so I lump them together. > > This is what went in: > > 2014-07-29 Jeff Layton <jlay...@poochiereds.net> > > [BZ #16839] > * manual/llio.texi: Add section about open file description > locks. > * manual/examples/ofdlocks.c: Example of open file description > lock usage. > * sysdeps/unix/sysv/linux/bits/fcntl-linux.h: Define > F_OFD_GETLK, F_OFD_SETLK, and F_OFD_SETLKW. > > As the committer I added #16839 to the fixed bug list following: > > https://sourceware.org/glibc/wiki/Committer%20checklist > > > --- > > manual/examples/ofdlocks.c | 77 +++++++++ > > manual/llio.texi | 241 > > ++++++++++++++++++++++++++++- > > sysdeps/unix/sysv/linux/bits/fcntl-linux.h | 17 ++ 3 files > > changed, 332 insertions(+), 3 deletions(-) create mode 100644 > > manual/examples/ofdlocks.c > > > > diff --git a/manual/examples/ofdlocks.c b/manual/examples/ofdlocks.c > > new file mode 100644 > > index 000000000000..85e193cdabe6 > > --- /dev/null > > +++ b/manual/examples/ofdlocks.c > > @@ -0,0 +1,77 @@ > > +/* Open File Description Locks Usage Example > > + Copyright (C) 1991-2014 Free Software Foundation, Inc. > > + > > + This program is free software; you can redistribute it and/or > > + modify it under the terms of the GNU General Public License > > + as published by the Free Software Foundation; either version 2 > > + of the License, or (at your option) any later version. > > + > > + This program is distributed in the hope that it will be useful, > > + but WITHOUT ANY WARRANTY; without even the implied warranty of > > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > + GNU General Public License for more details. > > + > > + You should have received a copy of the GNU General Public > > License > > + along with this program; if not, see > > <http://www.gnu.org/licenses/>. +*/ > > + > > +#define _GNU_SOURCE > > +#include <stdio.h> > > +#include <sys/types.h> > > +#include <sys/stat.h> > > +#include <unistd.h> > > +#include <fcntl.h> > > +#include <pthread.h> > > + > > +#define FILENAME "/tmp/foo" > > +#define NUM_THREADS 3 > > +#define ITERATIONS 5 > > + > > +void * > > +thread_start (void *arg) > > +{ > > + int i, fd, len; > > + long tid = (long) arg; > > + char buf[256]; > > + struct flock lck = { > > + .l_whence = SEEK_SET, > > + .l_start = 0, > > + .l_len = 1, > > + }; > > + > > + fd = open ("/tmp/foo", O_RDWR | O_CREAT, 0666); > > + > > + for (i = 0; i < ITERATIONS; i++) > > + { > > + lck.l_type = F_WRLCK; > > + fcntl (fd, F_OFD_SETLKW, &lck); > > + > > + len = sprintf (buf, "%d: tid=%ld fd=%d\n", i, tid, fd); > > + > > + lseek (fd, 0, SEEK_END); > > + write (fd, buf, len); > > + fsync (fd); > > + > > + lck.l_type = F_UNLCK; > > + fcntl (fd, F_OFD_SETLK, &lck); > > + > > + /* sleep to ensure lock is yielded to another thread */ > > + usleep (1); > > + } > > + pthread_exit (NULL); > > +} > > + > > +int > > +main (int argc, char **argv) > > +{ > > + long i; > > + pthread_t threads[NUM_THREADS]; > > + > > + truncate (FILENAME, 0); > > + > > + for (i = 0; i < NUM_THREADS; i++) > > + pthread_create (&threads[i], NULL, thread_start, (void *) i); > > + > > + pthread_exit (NULL); > > + return 0; > > +} > > diff --git a/manual/llio.texi b/manual/llio.texi > > index 6f8adfc607d7..864060dc7140 100644 > > --- a/manual/llio.texi > > +++ b/manual/llio.texi > > @@ -57,6 +57,10 @@ directly.) > > flags associated with > > open files. > > * File Locks:: Fcntl commands for > > implementing file locking. > > +* Open File Description Locks:: Fcntl commands for > > implementing > > + open file description > > locking. +* Open File Description Locks Example:: An example of > > open file description lock > > + usage > > * Interrupt Input:: Getting an asynchronous > > signal when input arrives. > > * IOCTLs:: Generic I/O Control > > operations. @@ -2890,7 +2894,7 @@ Get flags associated with the > > open file. @xref{File Status Flags}. Set flags associated with the > > open file. @xref{File Status Flags}. > > @item F_GETLK > > -Get a file lock. @xref{File Locks}. > > +Test a file lock. @xref{File Locks}. > > > > @item F_SETLK > > Set or clear a file lock. @xref{File Locks}. > > @@ -2898,6 +2902,18 @@ Set or clear a file lock. @xref{File Locks}. > > @item F_SETLKW > > Like @code{F_SETLK}, but wait for completion. @xref{File Locks}. > > > > +@item F_OFD_GETLK > > +Test an open file description lock. @xref{Open File Description > > Locks}. +Specific to Linux. > > + > > +@item F_OFD_SETLK > > +Set or clear an open file description lock. @xref{Open File > > Description Locks}. +Specific to Linux. > > + > > +@item F_OFD_SETLKW > > +Like @code{F_OFD_SETLK}, but block until lock is acquired. > > +@xref{Open File Description Locks}. Specific to Linux. > > + > > @item F_GETOWN > > Get process or process group ID to receive @code{SIGIO} signals. > > @xref{Interrupt Input}. > > @@ -3576,6 +3592,10 @@ set_nonblock_flag (int desc, int value) > > > > @cindex file locks > > @cindex record locking > > +This section describes record locks that are associated with the > > process. +There is also a different type of record lock that is > > associated with the +open file description instead of the process. > > @xref{Open File Description Locks}. + > > The remaining @code{fcntl} commands are used to support @dfn{record > > locking}, which permits multiple cooperating programs to prevent > > each other from simultaneously accessing parts of a file in > > error-prone @@ -3641,7 +3661,10 @@ the file. > > @item pid_t l_pid > > This field is the process ID (@pxref{Process Creation Concepts}) > > of the process holding the lock. It is filled in by calling > > @code{fcntl} with -the @code{F_GETLK} command, but is ignored when > > making a lock. +the @code{F_GETLK} command, but is ignored when > > making a lock. If the +conflicting lock is an open file > > description lock +(@pxref{Open File Description Locks}), then this > > field will be set to +@math{-1}. > > @end table > > @end deftp > > > > @@ -3813,10 +3836,222 @@ that part of the file for writing. > > > > @c ??? This section could use an example program. > > > > -Remember that file locks are only a @emph{voluntary} protocol for > > +Remember that file locks are only an @emph{advisory} protocol for > > controlling access to a file. There is still potential for access > > to the file by programs that don't use the lock protocol. > > > > +@node Open File Description Locks > > +@section Open File Description Locks > > + > > +In contrast to process-associated record locks (@pxref{File > > Locks}), +open file description record locks are associated with an > > open file +description rather than a process. > > + > > +Using @code{fcntl} to apply an open file description lock on a > > region that +already has an existing open file description lock > > that was created via the +same file descriptor will never cause a > > lock conflict. + > > +Open file description locks are also inherited by child processes > > across +@code{fork}, or @code{clone} with @code{CLONE_FILES} set > > +(@pxref{Creating a Process}), along with the file descriptor. > > + > > +It is important to distinguish between the open file > > @emph{description} (an +instance of an open file, usually created > > by a call to @code{open}) and +an open file @emph{descriptor}, > > which is a numeric value that refers to the +open file > > description. The locks described here are associated with the > > +open file @emph{description} and not the open file > > @emph{descriptor}. + +Using @code{dup} (@pxref{Duplicating > > Descriptors}) to copy a file +descriptor does not give you a new > > open file description, but rather copies a +reference to an > > existing open file description and assigns it to a new +file > > descriptor. Thus, open file description locks set on a file > > +descriptor cloned by @code{dup} will never conflict with open file > > +description locks set on the original descriptor since they refer > > to the +same open file description. Depending on the range and > > type of lock +involved, the original lock may be modified by a > > @code{F_OFD_SETLK} or +@code{F_OFD_SETLKW} command in this > > situation however. + +Open file description locks always conflict > > with process-associated locks, +even if acquired by the same > > process or on the same open file +descriptor. > > + > > +Open file description locks use the same @code{struct flock} as > > +process-associated locks as an argument (@pxref{File Locks}) and > > the +macros for the @code{command} values are also declared in the > > header file +@file{fcntl.h}. To use them, the macro > > @code{_GNU_SOURCE} must be +defined prior to including any header > > file. + > > +In contrast to process-associated locks, any @code{struct flock} > > used as +an argument to open file description lock commands must > > have the @code{l_pid} +value set to @math{0}. Also, when returning > > information about an +open file description lock in a > > @code{F_GETLK} or @code{F_OFD_GETLK} request, +the @code{l_pid} > > field in @code{struct flock} will be set to @math{-1} +to indicate > > that the lock is not associated with a process. + > > +When the same @code{struct flock} is reused as an argument to a > > +@code{F_OFD_SETLK} or @code{F_OFD_SETLKW} request after being used > > for an +@code{F_OFD_GETLK} request, it is necessary to inspect and > > reset the +@code{l_pid} field to @math{0}. > > + > > +@pindex fcntl.h. > > + > > +@deftypevr Macro int F_OFD_GETLK > > +This macro is used as the @var{command} argument to @code{fcntl}, > > to +specify that it should get information about a lock. This > > command +requires a third argument of type @w{@code{struct flock > > *}} to be passed +to @code{fcntl}, so that the form of the call is: > > + > > +@smallexample > > +fcntl (@var{filedes}, F_OFD_GETLK, @var{lockp}) > > +@end smallexample > > + > > +If there is a lock already in place that would block the lock > > described +by the @var{lockp} argument, information about that lock > > is written to +@code{*@var{lockp}}. Existing locks are not > > reported if they are +compatible with making a new lock as > > specified. Thus, you should +specify a lock type of @code{F_WRLCK} > > if you want to find out about both +read and write locks, or > > @code{F_RDLCK} if you want to find out about +write locks only. > > + > > +There might be more than one lock affecting the region specified > > by the +@var{lockp} argument, but @code{fcntl} only returns > > information about +one of them. Which lock is returned in this > > situation is undefined. + > > +The @code{l_whence} member of the @var{lockp} structure are set to > > +@code{SEEK_SET} and the @code{l_start} and @code{l_len} fields are > > set +to identify the locked region. > > + > > +If no conflicting lock exists, the only change to the @var{lockp} > > structure +is to update the @code{l_type} field to the value > > @code{F_UNLCK}. + > > +The normal return value from @code{fcntl} with this command is > > either @math{0} +on success or @math{-1}, which indicates an error. > > The following @code{errno} +error conditions are defined for this > > command: + > > +@table @code > > +@item EBADF > > +The @var{filedes} argument is invalid. > > + > > +@item EINVAL > > +Either the @var{lockp} argument doesn't specify valid lock > > information, +the operating system kernel doesn't support open file > > description locks, or the file +associated with @var{filedes} > > doesn't support locks. +@end table > > +@end deftypevr > > + > > +@comment fcntl.h > > +@comment POSIX.1 > > +@deftypevr Macro int F_OFD_SETLK > > +This macro is used as the @var{command} argument to @code{fcntl}, > > to +specify that it should set or clear a lock. This command > > requires a +third argument of type @w{@code{struct flock *}} to be > > passed to +@code{fcntl}, so that the form of the call is: > > + > > +@smallexample > > +fcntl (@var{filedes}, F_OFD_SETLK, @var{lockp}) > > +@end smallexample > > + > > +If the open file already has a lock on any part of the > > +region, the old lock on that part is replaced with the new lock. > > You +can remove a lock by specifying a lock type of @code{F_UNLCK}. > > + > > +If the lock cannot be set, @code{fcntl} returns immediately with a > > value +of @math{-1}. This command does not wait for other tasks > > +to release locks. If @code{fcntl} succeeds, it returns @math{0}. > > + > > +The following @code{errno} error conditions are defined for this > > +command: > > + > > +@table @code > > +@item EAGAIN > > +The lock cannot be set because it is blocked by an existing lock > > on the +file. > > + > > +@item EBADF > > +Either: the @var{filedes} argument is invalid; you requested a > > read lock +but the @var{filedes} is not open for read access; or, > > you requested a +write lock but the @var{filedes} is not open for > > write access. + > > +@item EINVAL > > +Either the @var{lockp} argument doesn't specify valid lock > > information, +the operating system kernel doesn't support open file > > description locks, or the +file associated with @var{filedes} > > doesn't support locks. + > > +@item ENOLCK > > +The system has run out of file lock resources; there are already > > too +many file locks in place. > > + > > +Well-designed file systems never report this error, because they > > have no +limitation on the number of locks. However, you must > > still take account +of the possibility of this error, as it could > > result from network access +to a file system on another machine. > > +@end table > > +@end deftypevr > > + > > +@comment fcntl.h > > +@comment POSIX.1 > > +@deftypevr Macro int F_OFD_SETLKW > > +This macro is used as the @var{command} argument to @code{fcntl}, > > to +specify that it should set or clear a lock. It is just like the > > +@code{F_OFD_SETLK} command, but causes the process to wait until > > the request +can be completed. > > + > > +This command requires a third argument of type @code{struct flock > > *}, as +for the @code{F_OFD_SETLK} command. > > + > > +The @code{fcntl} return values and errors are the same as for the > > +@code{F_OFD_SETLK} command, but these additional @code{errno} > > error conditions +are defined for this command: > > + > > +@table @code > > +@item EINTR > > +The function was interrupted by a signal while it was waiting. > > +@xref{Interrupted Primitives}. > > + > > +@end table > > +@end deftypevr > > + > > +Open file description locks are useful in the same sorts of > > situations as +process-associated locks. They can also be used to > > synchronize file +access between threads within the same process by > > having each thread perform +its own @code{open} of the file, to > > obtain its own open file description. + > > +Because open file description locks are automatically freed only > > upon +closing the last file descriptor that refers to the open file > > +description, this locking mechanism avoids the possibility that > > locks +are inadvertently released due to a library routine opening > > and closing +a file without the application being aware. > > + > > +As with process-associated locks, open file description locks are > > advisory. + > > +@node Open File Description Locks Example > > +@section Open File Description Locks Example > > + > > +Here is an example of using open file description locks in a > > threaded +program. If this program used process-associated locks, > > then it would be +subject to data corruption because > > process-associated locks are shared +by the threads inside a > > process, and thus cannot be used by one thread +to lock out another > > thread in the same process. + > > +Proper error handling has been omitted in the following program for > > +brevity. > > + > > +@smallexample > > +@include ofdlocks.c.texi > > +@end smallexample > > + > > +This example creates three threads each of which loops five times, > > +appending to the file. Access to the file is serialized via open > > file +description locks. If we compile and run the above program, > > we'll end up +with /tmp/foo that has 15 lines in it. > > + > > +If we, however, were to replace the @code{F_OFD_SETLK} and > > +@code{F_OFD_SETLKW} commands with their process-associated lock > > +equivalents, the locking essentially becomes a noop since it is > > all done +within the context of the same process. That leads to > > data corruption +(typically manifested as missing lines) as some > > threads race in and +overwrite the data written by others. > > + > > @node Interrupt Input > > @section Interrupt-Driven Input > > > > diff --git a/sysdeps/unix/sysv/linux/bits/fcntl-linux.h > > b/sysdeps/unix/sysv/linux/bits/fcntl-linux.h index > > 527eb5c8b5d9..b5b5d0fbfa4c 100644 --- > > a/sysdeps/unix/sysv/linux/bits/fcntl-linux.h +++ > > b/sysdeps/unix/sysv/linux/bits/fcntl-linux.h @@ -117,6 +117,23 @@ > > # define F_SETLKW64 14 /* Set record locking info > > (blocking). */ #endif > > > > +/* open file description locks. > > + > > + Usually record locks held by a process are released on *any* > > close and are > > + not inherited across a fork. > > + > > + These cmd values will set locks that conflict with > > process-associated record > > + locks, but are "owned" by the opened file description, not the > > process. > > + This means that they are inherited across fork or clone with > > CLONE_FILES > > + like BSD (flock) locks, and they are only released > > automatically when the > > + last reference to the the file description against which they > > were acquired > > + is put. */ > > +#if __USE_GNU > > This was changed back to `#ifdef' given Joseph's request to avoid > partial conversion of macro usages. > > > +# define F_OFD_GETLK 36 > > +# define F_OFD_SETLK 37 > > +# define F_OFD_SETLKW 38 > > +#endif > > + > > #ifdef __USE_LARGEFILE64 > > # define O_LARGEFILE __O_LARGEFILE > > #endif > > > > Cheers, > Carlos. -- Jeff Layton <jlay...@primarydata.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
