Date: Sat, 25 Apr 2015 10:50:40 +0800 From: Julian Elischer <julian@freebsd.org> To: Jilles Tjoelker <jilles@stack.nl>, John Baldwin <jhb@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: readdir/telldir/seekdir problem (i think) Message-ID: <553B0100.4070307@freebsd.org> In-Reply-To: <20150424215249.GA96554@stack.nl> References: <55386505.70708@freebsd.org> <553A7DB0.8080308@freebsd.org> <553A8D28.7090901@freebsd.org> <4718551.Y2ZnMk6NSM@ralph.baldwin.cx> <20150424215249.GA96554@stack.nl>
next in thread | previous in thread | raw e-mail | index | archive | help
On 4/25/15 5:52 AM, Jilles Tjoelker wrote: > On Fri, Apr 24, 2015 at 04:28:12PM -0400, John Baldwin wrote: >> Yes, this isn't at all safe. There's no guarantee whatsoever that >> the offset on the directory fd that isn't something returned by >> getdirentries has any meaning. In particular, the size of the >> directory entry in a random filesystem might be a different size >> than the structure returned by getdirentries (since it converts >> things into a FS-independent format). >> This might work for UFS by accident, but this is probably why ZFS >> doesn't work. >> However, this might be properly fixed by the thing that ino64 is >> doing where each directory entry returned by getdirentries gives >> you a seek offset that you _can_ directly seek to (as opposed to >> seeking to the start of the block and then walking forward N >> entries until you get an inter-block entry that is the same). > The ino64 branch only reserves space for d_off and does not use it in > any way. This is appropriate since actually using d_off is a major > feature addition. > > A proper d_off would still be useful even if UFS's readdir keeps masking > off the offset so a directory read always starts at the beginning of a > 512-byte directory block, since this allows more distinct offset values > than safely using getdirentries()'s *basep. With d_off, one outer loop > must read at least one directory block to avoid spinning indefinitely, > while using getdirentries()'s *basep requires reading the whole > getdirentries() buffer. > > Some Linux filesystems go further and provide a unique d_off for each > entry. > > Another idea would be to store the last d_ino instead of dd_loc into the > struct ddloc. On seekdir(), this would seek to loc_seek as before and > skip entries until that d_ino is found, or to the start of the buffer if > not found (and possibly return some entries again that should not be > returned, but Samba copes with that). yes.. though maybe a hash of hte inode number and the name may be a better thing to search on.. I need to check on your statement about samba to see if its true for 3.6.. >
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?553B0100.4070307>