From: ebiederm@xmission.com (Eric W. Biederman) To: David Howells <dhowells@redhat.com> Cc: Karel Zak <kzak@redhat.com>, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Al Viro <viro@ZenIV.linux.org.uk>, Miklos Szeredi <miklos@szeredi.hu>, Linus Torvalds <torvalds@linux-foundation.org>, util-linux@vger.kernel.org, Andy Lutomirski <luto@amacapital.net> Subject: Re: [RFD] A mount api that notices previous mounts Date: Wed, 30 Jan 2019 07:35:39 -0600 [thread overview] Message-ID: <87h8dqs1xw.fsf@xmission.com> (raw) In-Reply-To: <9871.1548853314@warthog.procyon.org.uk> (David Howells's message of "Wed, 30 Jan 2019 13:01:54 +0000") David Howells <dhowells@redhat.com> writes: > Karel Zak <kzak@redhat.com> wrote: > >> It seems more elegant is to ask for Nth option as expected by fsinfo(). > > More elegant yes, but there's an issue with atomiticity[*]. I'm in the > process of switching to something that returns you a single buffer with all > the options in, but each key and each value is preceded by a length count. > > The reasons for not using separator characters are: > > (1) There's no separator char that cannot validly occur within an option[**]. *Blink* I had missed the cifs issue. So yes we certainly need a better way to encode things in the buffer. I just used a single string as an easy way to place everything in a buffer. > (2) Makes it possible to return binary values if we need to. I don't totally disagree with this. But I will point out that except for coda passing a file descriptor there are no filesystems that currently take or need binary options. I suspect that as long as userspace supports /etc/fstab and we in turn support /proc/mounts there is going to be a lot of pressure to keep the majority of options so they can be encoded in a string separated by commas. > David > > [*] Atomic with respect to remount calls, that is. There are also mount options that depend on each other and whose order matters with respect to other mount options extN's ("sb=<NNNN>") for example. > [**] Oh, and look at cifs where you can *change* the separator char during > option parsing ("sep=<char>").
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From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) To: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Cc: Karel Zak <kzak-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Miklos Szeredi <miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, util-linux-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org> Subject: Re: [RFD] A mount api that notices previous mounts Date: Wed, 30 Jan 2019 07:35:39 -0600 [thread overview] Message-ID: <87h8dqs1xw.fsf@xmission.com> (raw) In-Reply-To: <9871.1548853314-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org> (David Howells's message of "Wed, 30 Jan 2019 13:01:54 +0000") David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> writes: > Karel Zak <kzak-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote: > >> It seems more elegant is to ask for Nth option as expected by fsinfo(). > > More elegant yes, but there's an issue with atomiticity[*]. I'm in the > process of switching to something that returns you a single buffer with all > the options in, but each key and each value is preceded by a length count. > > The reasons for not using separator characters are: > > (1) There's no separator char that cannot validly occur within an option[**]. *Blink* I had missed the cifs issue. So yes we certainly need a better way to encode things in the buffer. I just used a single string as an easy way to place everything in a buffer. > (2) Makes it possible to return binary values if we need to. I don't totally disagree with this. But I will point out that except for coda passing a file descriptor there are no filesystems that currently take or need binary options. I suspect that as long as userspace supports /etc/fstab and we in turn support /proc/mounts there is going to be a lot of pressure to keep the majority of options so they can be encoded in a string separated by commas. > David > > [*] Atomic with respect to remount calls, that is. There are also mount options that depend on each other and whose order matters with respect to other mount options extN's ("sb=<NNNN>") for example. > [**] Oh, and look at cifs where you can *change* the separator char during > option parsing ("sep=<char>").
next prev parent reply other threads:[~2019-01-30 13:35 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-01-29 21:44 [RFD] A mount api that notices previous mounts Eric W. Biederman 2019-01-29 21:44 ` Eric W. Biederman 2019-01-29 23:01 ` Casey Schaufler 2019-01-29 23:01 ` Casey Schaufler 2019-01-30 1:15 ` Eric W. Biederman 2019-01-30 1:23 ` Eric W. Biederman 2019-01-30 1:23 ` Eric W. Biederman 2019-01-30 12:47 ` Eric W. Biederman 2019-01-30 16:19 ` Casey Schaufler 2019-01-30 16:19 ` Casey Schaufler 2019-01-30 12:06 ` Karel Zak 2019-01-30 12:06 ` Karel Zak 2019-01-30 13:45 ` Eric W. Biederman 2019-01-30 12:50 ` David Howells 2019-01-30 12:50 ` David Howells 2019-01-30 13:24 ` Eric W. Biederman 2019-01-30 13:24 ` Eric W. Biederman 2019-01-30 13:01 ` David Howells 2019-01-30 13:35 ` Eric W. Biederman [this message] 2019-01-30 13:35 ` Eric W. Biederman 2019-01-30 18:00 ` Karel Zak 2019-01-30 17:43 ` Karel Zak
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