Copying Volker; maybe he has some thoughts about how this might work with Samba on Linux. > On Oct 6, 2024, at 2:53 AM, Cedric Blancher <cedric.blancher@xxxxxxxxx> wrote: > > Good morning! > > Windows Server 2022 has a NFS export option called > "HideFilesBeginningInDot", which sets the NFS WORD0_HIDDEN flag if a > file starts with a '.' character. > https://learn.microsoft.com/en-us/powershell/module/nfs/set-nfsserverconfiguration?view=windowsserver2022-ps > has some documentation on this. > > We'd like to get the same functionality for Linux nfsd, enabled by > default ("NoHideFilesBeginningInDot" to turn it off), as a mount > option. I'm assuming you mean "export option" here, not "mount option." I'm not sure whether enabling the new behavior by default is OK, by Linux rules of not introducing behavior regressions. Will ponder. > Before I start writing a patch, are there any objections? Not an objection, but here are some things to consider as you prototype. You might be planning to store this not as an actual file attribute (retrieved via vfs_getattr or vfs_getxattr) but instead NFSD would construct attribute 25 based on whether the file name begins with dot and the new export option is set. On Linux, file names are kept in the parent directory, not with the file; and note that a file can have more than one name (directory entry) that refers to it. Thus it might be difficult to retrieve the file's name inside of nfsd4_getattr(), let alone retrieve it efficiently, since GETATTR is a frequent operation. You will need a deterministic mechanism to resolve the ambiguity if the file has multiple names, only some of which begin with a dot. Maybe -- only if all of the file's names begin with a dot, then it is marked HIDDEN? You will have to do something about SETATTR. RFC 8881 shows that HIDDEN is a r/w attribute, and IIUC what you are proposing is a r/o attribute -- clients cannot change this setting via SETATTR. I'm not sure, but probably NFSD's SETATTR will need to clear the HIDDEN bit and otherwise ignore it. I haven't found any spec language that addresses how a server needs to behave if it supports a RECOMMENDED r/w attribute but does not permit it to be modified by clients. Given these issues, perhaps that explains why the Microsoft documentation you provided says only: "Specifies whether an NFS server creates files that have names that begin with a dot (.) as hidden files." That is, it appears that the Windows server sets the HIDDEN attribute on the file inode at creation time. That has it's own set of issues for Linux, since our file systems don't implement a HIDDEN attribute (that I know of). -- Chuck Lever
