From owner-freebsd-current@freebsd.org Wed May 22 20:57:42 2019 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 7583215B7273 for ; Wed, 22 May 2019 20:57:42 +0000 (UTC) (envelope-from johalun@FreeBSD.org) Received: from smtp.freebsd.org (smtp.freebsd.org [IPv6:2610:1c1:1:606c::24b:4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "smtp.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 15AD769D66; Wed, 22 May 2019 20:57:42 +0000 (UTC) (envelope-from johalun@FreeBSD.org) Received: from [10.46.14.95] (wsip-72-212-151-146.ph.ph.cox.net [72.212.151.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client did not present a certificate) (Authenticated sender: johalun) by smtp.freebsd.org (Postfix) with ESMTPSA id 7F85614C85; Wed, 22 May 2019 20:57:41 +0000 (UTC) (envelope-from johalun@FreeBSD.org) Subject: Re: Weirdness when writing to pseudofs file From: Johannes Lundberg To: Alan Somers Cc: Konstantin Belousov , FreeBSD Current References: <6ec62e4d-9f93-ffe1-646c-3846c9308334@FreeBSD.org> <20190522175133.GC2748@kib.kiev.ua> <84e3001b-646d-b1d9-f206-577d63f79bf1@FreeBSD.org> Openpgp: preference=signencrypt Autocrypt: addr=johalun@FreeBSD.org; keydata= mQENBFxF1scBCADCZ7FGn5McAhF+lMDAFtnLpibJmyUIfcrqy7uSbZEBoJJSwAjgfjE29oAl 4p8sT95NBxosqIX0YG/x9EtAeIJFIU3BefEhlZLzQIop+931uxlwyhjRsfUVtver9MYcOKyd P85ig7ZhDcSM59MTLO1UeqGEhYAawVbVK05XAfEpQjkgPM7huIKDseECT3yPDI+0cDm2f9dy GN3nUuhDS9/SYrSkCIhHchF4iPwM7pB2IXUBK9ZQ2Fga9ga3dMVXiqYv2xHblXgVy4t81kD/ 4pt2dNlt+/w2XVIINLs8Hb6LFqR6xHsUu+szH0yHh2iBOWWFngFnv+FNL7UxtN1Wh6xNABEB AAG0J0pvaGFubmVzIEx1bmRiZXJnIDxqb2hhbHVuQEZyZWVCU0Qub3JnPokBVAQTAQoAPhYh BJOkM69EHGnBp2zy0eoSxwPvo3npBQJcRdbHAhsDBQkFo5qABQsJCAcDBRUKCQgLBRYDAgEA Ah4BAheAAAoJEOoSxwPvo3npml0H/0ugSyugyG8bwwlV3BBkauhH2x6lTu4xMKUBJWyk7Uu7 lGgKVjZp08ivvU0KDYQcvWfVnJ5aqYDqUPf+LwfyDyzALt0AKU9MXmSJXJDuABskoDOsh3iX uH4Rp9B+GtXoV5lfyddDxvC6htag7GxVpwZQVmGuPt2G8CZhSp2xlD5VAGFriKILV2NCiJ6O c1xIw6sIbaXLi9iykVlVaH1/w3lgknhAmPOK+sgIqMqVFnD2GcIv9VE5V/ZKgIUS3k6B0Vas +GfNUJkM9wzrEvYfiL4za0ARzy6RXM5RO9b5UHN51Eg39ti18/J17Q54vd1LP0WBDboBjw3X tGrd26vCap65AQ0EXEXWxwEIAJzhUuViNsqv/INGxCOAcF81b4NVH4qmM7pa5ukf8v+HtNrm Obwp/c0UaZV4G2wgg7PCSA9rF+5Y8yW7E/G4YxNgvsWl4ES9kzh67oahZQSUlGqc1m23IiyL 5lcWop4KSk6qCAzG+d+67MJH92jz8gzwJjGqRZZ4y6D6Et9/u2srKpUT1jsXi18Rg6La+nvd FP+5n5+CMjE2zJpnY5hB5Yd4QURsMiUeta+NBi9f4fOYJhNUBfDg8AAFLWCtnoJJ6Mn6TXOO N/BkKDSqJkMAR04TLWTpUJFhzhS5cM/g95g9Xjr5SErdw+a/t6WIGeLaeOKcXOgiLhO4rKJ/ rLv8WnMAEQEAAYkBPAQYAQoAJhYhBJOkM69EHGnBp2zy0eoSxwPvo3npBQJcRdbHAhsMBQkF o5qAAAoJEOoSxwPvo3npR0IIAI/4I0I+AWHk5JZGEpodWVjcS07XPB//qS1nmPkIDmR6AFeS +515D5u37C2xjMGdPIuS8TCmt2fEwcgXH+ZHTOeIjSM5XA6rp+xLS3NN9HOkPVvhAI78Qzi3 zXqsyRmg/m8DyQTBFuLkyPUOtNkFvcEjXkHuieRJoif8WsOZXm5FM3CvSno9mDys7o2RDsNY is4R6byGNxqq013Jrui+6nwqXlmyk7ZUzv8lm0rsUgLFIXq4ZoWkTBMpphEYFkL4NITyMHIO NgMTprpHf68yqdhv+6m53BFhdnyDrTUOITJyzMmSzQtr+KoT4RLbBknY0RbLtGA44PsO1i2o EOfvGKE= X-Tagtoolbar-Keys: D20190522135740634 Message-ID: Date: Wed, 22 May 2019 13:57:40 -0700 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Rspamd-Queue-Id: 15AD769D66 X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org X-Spamd-Result: default: False [-2.96 / 15.00]; local_wl_from(0.00)[FreeBSD.org]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; NEURAL_HAM_SHORT(-0.97)[-0.965,0]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; ASN(0.00)[asn:11403, ipnet:2610:1c1:1::/48, country:US] Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 May 2019 20:57:42 -0000 On 5/22/19 1:53 PM, Johannes Lundberg wrote: > On 5/22/19 11:03 AM, Alan Somers wrote: >> On Wed, May 22, 2019 at 11:59 AM Johannes Lundberg wrote: >>> On 5/22/19 10:51 AM, Konstantin Belousov wrote: >>>> On Wed, May 22, 2019 at 10:36:34AM -0700, Johannes Lundberg wrote: >>>>> Hi >>>>> >>>>> I'm fiddling with lindebugfs, which is based on pseudofs. When writing >>>>> to a file, >>>>> >>>>> this works: # echo 1 >> /path/to/file >>>>> >>>>> but this does not: # echo 1 > /path/to/file >>>>> >>>>> "Operation not supported." is returned before the pseudofs code is even >>>>> entered. >>>>> >>>>> Is this expected behavior? (if so, why?) >>>> Does the file exist ? >>>> >>>> Pseudofs does not implement VOP_CREATE(), which is reasonable. >>> Yes, it exists and my custom write function is receiving the call for >>> ">>". (which is for example used by drm driver debugfs to do certain >>> things on demand by accepting write to a debugfs file) >> First, you need to try ktrace to see exactly which system call is not >> supported. If the problem still isn't obvious, then you can try >> dtrace to see exactly which VOP isn't suppoted. Do it like this: >> >> sudo ktrace /bin/sh -c "echo 1 > /path/to/file" >> sudo kdump >> sudo dtrace -i 'fbt:::return /arg1 == 45/ {trace(".")}' -c "/bin/sh -c >> 'echo 1 > /path/to/file/'" >> >> The dtrace command will show you which function returned EOPNOTSUPP. >> However, it will also show a lot of functions that coincidentally >> return 45 even though it's not an errno, and even functions that >> return void. >> >> -Alan > > Thanks! > > It seems, a single '>' will cause it to try to create the file (even > though it already exists) and that fails (kern_openat). > I would guess because of https://github.com/freebsd/freebsd/blob/master/sys/fs/pseudofs/pseudofs_vnops.c#L1042 struct vop_vector pfs_vnodeops = { ... .vop_create = VOP_EOPNOTSUPP, ... }