| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <10C5890F8F477E959B993BFA@nimrod.local> Date: Thu, 19 May 2011 16:06:27 +0100 From: Alex Bligh <alex@...x.org.uk> To: linux-kernel@...r.kernel.org cc: Alex Bligh <alex@...x.org.uk> Subject: REQ_FLUSH, REQ_FUA and open/close of block devices I am doing some work on making REQ_FLUSH and REQ_FUA work with block devices and have some patches that make them perform as expected with nbd if an nbd device is mounted (e.g. -t ext3, -odata-journal,barriers=1), and I see the relevant REQ_FLUSH and REQ_FUA appearing much as expected. However, if I do a straight dd to the device (which generates an open() and a close()), I see no barrier activity at all (i.e. no REQ_FLUSH and no REQ_FUA). It is surprising to me that a close() on a raw device does not generate a REQ_FLUSH. I cannot imagine it is a performance overhead. I would have thought this would useful anyway (if I've written to a raw device I'd rather expect it to hit it when I do the close()), but my specific application is ensuring cache coherency on live migrate of virtual servers: if migrating from node A to node B, then when the hypervisor closes the block device on node A, I want to be sure that any locally cached write data is written to the remote disk before it unfreezes node B. Should a close() of a dirty block device result in a REQ_FLUSH? -- Alex Bligh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists