On 5/6/19 5:05 AM, Florian Weimer wrote: > I've been told that on Linux, close does not report writeback errors. > So the only way to get a reliable error indicator (beyond what you get > from the write system call) would be fsync.
Are you sure you asked your expert the right question? I just looked at the current (5.1) Linux kernel, and though I'm no kernel expert it looks like the close system call invokes filp_close, which calls filp->f_op->flush which on NFS is nfs_file_flush, which invokes vfs_fsync which in turn invokes nfs_file_fsync, and surely this does what fsync would do (and does more work and error checking than an ordinary write syscall would do, at any rate). Admittedly Linux is a real mess in reporting write errors back to the user, and this has been true for years.[1] That being said, the longstanding documented tradition is that writeback errors are reported in later close or fsync calls, and there are suggestions to clean up this kernel area to get closer to doing what the documentation says.[2] So until we're pretty sure the matter is settled for Linux, perhaps we'd better let Gnulib be. [1] Gunawi HS, Rubio-González C, Arpaci-Dusseau AC, Arpaci-Dusseau RH, Liblit B. EIO: Error Handling is Occasionally Correct. FAST 2008. https://www.usenix.org/legacy/event/fast08/tech/gunawi.html [2] Edge J. Handling writeback errors. LWN.net. 2017-05-04. https://lwn.net/Articles/718734/
