Date: Mon, 11 Mar 2002 10:34:55 +0100 (CET) From: Harti Brandt <brandt@fokus.gmd.de> To: Garance A Drosihn <drosih@rpi.edu> Cc: Poul-Henning Kamp <phk@critter.freebsd.dk>, <arch@FreeBSD.ORG> Subject: Re: Increasing the size of dev_t and ino_t Message-ID: <20020311102511.M516-100000@beagle.fokus.gmd.de> In-Reply-To: <p05101537b8b1707a3659@[128.113.24.47]>
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On Sun, 10 Mar 2002, Garance A Drosihn wrote: GAD>First, my starting assumption on the significance of the st_dev GAD>value. My take on that value is that if two files have the same GAD>value for their device, then you could remove one of those files GAD>and hardlink the other file to the name of the removed file. GAD>Hardlinks can not cross device boundaries, but if these two files GAD>have the same value for st_dev then that hard link would not be GAD>crossing a device boundry. Or, another way to think of it is that GAD>if two files have the same device-number, and if they both have an GAD>st_nlink count of 1, then removing one of those files will result GAD>in more space being available for the expansion of the other file. GAD>(perhaps after a reboot, to eliminate the question of open file GAD>descriptors keeping that first file around even though you have GAD>unlinked it). I do not know if the appropriate standards would GAD>agree with me on these views, but they seem like a logical premise. GAD>Otherwise, a st_dev value would have no special meaning at all. There is an explicit requirement in POSIX: it requires a given st_ino/st_dev pair to uniqely identify a file. I take this to mean: if two files have the same st_ino/st_dev pair, they are the same file. If I mount the same volume in different places in the tree any file on that volume must have the same st_ino/st_dev pair in both mount points. As worded by POSIX the st_ino/st_dev pairs are not required to be persistant through reboots. It can, however, be hard to implement persistant file handles for NFS based on non-persistant st_info/st_dev pairs. harti -- harti brandt, http://www.fokus.gmd.de/research/cc/cats/employees/hartmut.brandt/private brandt@fokus.fhg.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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