From: Jeff Hostetler Date: Fri, 04 Mar 2022 23:40:27 GMT Subject: Re: [PATCH 02/23] t7527: test FS event reporing on macOS WRT case and Unicode Message-ID: <8a32ed13-ed53-3605-ca78-83dac2be1e28@jeffhostetler.com> In-Reply-To: <20220224173305.gbr2waw77xpuieub@tb-raspi4> On 2/24/22 12:33 PM, Torsten =?unknown-8bit?Q?B=C3=B6gershausen?= wrote: > On Thu, Feb 24, 2022 at 09:52:28AM -0500, Derrick Stolee wrote: >> On 2/15/2022 10:59 AM, Jeff Hostetler via GitGitGadget wrote: >>> From: Jeff Hostetler >>> >>> Confirm that macOS FS events are reported with a normalized spelling. >>> >>> APFS (and/or HFS+) is case-insensitive. This means that case-independent > > This is not true, strictly speaking. > You can format a disk with "case sensitive" or "case-insenstive, case preserving". > Both APFS and HFS+ can be formated that way. > The default, which is what you get when you get a new machine, > is "case-insenstive, case preserving". > And I assume, that more 99% of all disks are formated that way. > The "core.ignorecase" is used in the same way as it is used under NTFS, > FAT or all other case-insenstive file systems. > (and even ext4 can be formated case-insensitive these days.) > > An interesting article can be found here: > https://lwn.net/Articles/784041/ > > And to be technically correct, I think that even NTFS can be > "configured to be case insensitive in an empty directory". > > In that sense, I would like to avoid this statement, which > file system is case insensitive, and which is not. > Git assumes that after probing the FS in "git init" we have > a valid configuration in core.ignorecase. You're right. I was incorrectly glossing over the differences between APFS and HFS+ -- and conflating case and nfc/nfd issues. [...] >> >>> NEEDSWORK: I was only able to test case. It would be nice to add tests >> >> "I was only able test the APFS case."? I'm going to completely redo this commit in the next version. I now have both APFS and HFS+ partitions on my machine and can compare the differences in behaviors and will have a new set of tests to cover this. >> >>> that use different Unicode spellings/normalizations and understand the >>> differences between APFS and HFS+ in this area. We should confirm that >>> the spelling of the workdir paths that the daemon sends to clients are >>> always properly normalized. >> >> Are there any macOS experts out there who can help us find the answers >> to these questions? > > There is a difference between HFS+ and APFS. > HFS+ is "unicode decomposing" when you call readdir() - file names > are stored decomposed on disk once created. > However, opening file in precompsed form succeds. > In that sense I would strongly suspect, that any monitors are "sending" > the decomposed form (on HFS+). > > APFS does not manipulate file names in that way, it is > "unicode normalization preserving and ignoring". It took a few hours of poking to figure out what Apple is doing, but yes on HFS+ they convert to NFD and use that as the on-disk format. And they do collision detection as they always have in NFD-space. Whereas on APFS, they preserve the NFC/NFD as given when the file is created, but always do the same collision detection in NFD-space. The net result is similar, but subtlety different. FS Events from MacOS are sent using the on-disk format (NFD on HFS+ and whichever on APFS) and my FSMonitor daemon is sending them to the client as received. I'm not sure whether or not the daemon should respect the `core.precompseUnicode` setting and when watching an HFS+ volume do the NFD-->NFC conversion for the client. I'm not sure whether that would be any more or less correct than just reporting the paths as received. I'm going to leave this as a question for the future. Thanks for all of your background information on this topic. Jeff