From: Aurelien Aptel <aaptel@xxxxxxxx> CIFS flock() locks behave differently than the standard. Give overview of those differences. Here is the rendered text: CIFS details In Linux kernels up to 5.4, flock() is not propagated over SMB. A file with such locks will not appear locked for remote clients. Since Linux 5.5, flock() locks are emulated with SMB byte-range locks on the entire file. Similarly to NFS, this means that fcntl(2) and flock() locks interact with one another. Another important side-effect is that the locks are not advisory anymore: any IO on a locked file will always fail with EACCES when done from a separate file descriptor. This difference originates from the design of locks in the SMB proto- col, which provides mandatory locking semantics. Remote and mandatory locking semantics may vary with SMB protocol, mount options and server type. See mount.cifs(8) for additional infor- mation. Signed-off-by: Aurelien Aptel <aaptel@xxxxxxxx> Discussion: linux-man <https://lore.kernel.org/linux-man/20210302154831.17000-1-aaptel@xxxxxxxx/> Signed-off-by: Alejandro Colomar <alx.manpages@xxxxxxxxx> --- man2/flock.2 | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/man2/flock.2 b/man2/flock.2 index 328377365..61822c9bc 100644 --- a/man2/flock.2 +++ b/man2/flock.2 @@ -239,6 +239,31 @@ see the discussion of the .I "local_lock" option in .BR nfs (5). +.SS CIFS details +In Linux kernels up to 5.4, +.BR flock () +is not propagated over SMB. +A file with such locks will not appear locked for remote clients. +.PP +Since Linux 5.5, +.BR flock () +locks are emulated with SMB byte-range locks on the entire file. +Similarly to NFS, this means that +.BR fcntl (2) +and +.BR flock () +locks interact with one another. +Another important side-effect is that the locks are not advisory anymore: +any IO on a locked file will always fail with +.BR EACCES +when done from a separate file descriptor. +This difference originates from the design of locks in the SMB protocol, +which provides mandatory locking semantics. +.PP +Remote and mandatory locking semantics may vary with SMB protocol, mount options and server type. +See +.BR mount.cifs (8) +for additional information. .SH SEE ALSO .BR flock (1), .BR close (2), -- 2.31.1
