On Tue, Jan 9, 2018 at 11:44 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > On Tue, Jan 9, 2018 at 12:07 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >> On Tue, Jan 9, 2018 at 10:54 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: >>> On Tue, Jan 9, 2018 at 11:16 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >>>> On Thu, Jan 4, 2018 at 5:40 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: >>>>> Introduce the "verify" config, module and mount options. >>>>> >>>>> If the "verify" feature is enabled then overlay filesystems will use >>>>> the inodes index dir to verify layers consistency. >>>>> >>>>> It is possible to enable consistency verification by default during >>>>> build time with the OVERLAY_FS_VERIFY config option, during runtime >>>>> with the "verify=on" module option or on a filesystem instance basis >>>>> with the "verify=on" mount option. >>>>> >>>>> The "verify" feature will prevent multiple redirects to the same lower >>>>> dir and will prevent broken hardlinks from using the same inode number. >>>>> >>>>> On an overlay filesystem instance with multiple lower layers, "verify" >>>>> feature can only use the index to prevent multiple redirects from upper >>>>> dirs and not from middle layer dirs. Emit a warning about this on mount >>>>> with multiple lower layers and "verify=on". >>>> >>>> Could the above go into Documentation/filesystems/overlayfs.txt as well? >>> >>> Will do. >>> BTW, are you ok with the feature name "verify" or do you prefer that >>> I rename it to "verify_origin" to be more descriptive as Vivek suggested? >>> >>>> >>>> Also, the verify feature does have some overhead, which should also be >>>> noted in the documentation. Do you have some measurements about how >>>> much impact it has on performance? >>>> >>> >>> I do not. It's on my TODO list. >>> >>> I'm curious though, where do you think it should performance? >>> I would expect that encoding a file handle and index lookup would not be >>> that expensive, so I don't expect much lookup overhead. No? >> >> I wasn't thinking about anything specific, but now you ask: >> directories always need to be connected, and that results in multiple >> readdirs, etc, that is probably noticeable under some conditions. >> > > Right. For the record, there is no decoding of directory file handles > with verify=on expect for ovl_indexdir_cleanup() that could become > optional and expect for decoding an overlay dir file handle for nfsd > of course. Ah, okay. > > The feature that does decoding of file handles on lookup for snapshots > was separated (per your request) to a different opt-in mount option: > https://github.com/amir73il/linux/commits/ovl-redirect-origin > and is not included in this posting. Yes, I remember now. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
