If an advisory lock is lost, then read/write requests on any affected file descriptor can return EIO - for NFSv4 at least. Signed-off-by: NeilBrown <neilb@xxxxxxxx> --- man2/fcntl.2 | 24 ++++++++++++++++++++++++ man2/read.2 | 9 +++++++++ man2/write.2 | 9 +++++++++ 3 files changed, 42 insertions(+) diff --git a/man2/fcntl.2 b/man2/fcntl.2 index 67642384154c..6e6e26f66aa0 100644 --- a/man2/fcntl.2 +++ b/man2/fcntl.2 @@ -669,6 +669,30 @@ and Mandatory locking is not specified by POSIX. Some other systems also support mandatory locking, although the details of how to enable it vary across systems. +.SS Lost locks +When an advisory lock is obtained on a networked filesystem such as +NFS it is possible that the lock might get lost. +This may happen due to administrative action on the server, or due to a +network partition which lasts long enough for the server to assume +that the client is no longer functioning. +.PP +When the filesystem determines that a lock has been lost, future +.BR read (2) +or +.BR write (2) +requests may fail with the error +.BR EIO . +This error will persist until the lock is removed or the file +descriptor is closed. +Since Linux 3.12, +.\" commit ef1820f9be27b6ad158f433ab38002ab8131db4d +this happens at least for NFSv4 including all minor versions. +.PP +Some versions of Unix send a signal +.RB ( SIGLOST ) +in this circumstance. +Linux does not define this signal, and does not provide any +asynchronous notification of lost locks. .SS Managing signals .BR F_GETOWN , .BR F_SETOWN , diff --git a/man2/read.2 b/man2/read.2 index f2e1379865df..0fea86e523a5 100644 --- a/man2/read.2 +++ b/man2/read.2 @@ -163,6 +163,15 @@ or its process group is orphaned. It may also occur when there is a low-level I/O error while reading from a disk or tape. +A further possible cause of +.B EIO +on networked filesystems is when an advisory lock had been taken +out on the file descriptor and this lock has been lost. +See the +.I "Lost locks" +section of +.BR fcntl (2) +for further details. .TP .B EISDIR .I fd diff --git a/man2/write.2 b/man2/write.2 index 796cae8ba221..621a484dc3a2 100644 --- a/man2/write.2 +++ b/man2/write.2 @@ -197,6 +197,15 @@ be reported by a subsequent (whether or not they were also reported by .BR write (2)). .\" commit 088737f44bbf6378745f5b57b035e57ee3dc4750 +An alternate cause of +.B EIO +on networked filesystems is when an advisory lock had been taken out +on the file descriptor and this lock has been lost. +See the +.I "Lost locks" +section of +.BR fcntl (2) +for further details. .TP .B ENOSPC The device containing the file referred to by -- 2.14.0.rc0.dirty
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