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On 17. 1. 2010 11:30, Alan McKinnon wrote: |
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>> In between I got a reply from other mailing list saying |
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>> "it is not a bug, it is a feature!". And the reason for |
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>> this feature is udev - it creates dev-files dynamically |
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>> and sata port-numbers do not play any role for order |
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>> in which hard-drives are detected and dev-file created. |
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>> Maybe some udev-expert here could explain in which |
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>> order udev writes device-files for hard-disks (maybe |
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>> serial number, or vendor name?)... |
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> |
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> Generally it's the order they are found in. |
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> |
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> udev gives you the ability to dynamically create only the nodes you need |
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> without having to worry if you've left something out of MAKEDEV. To do this, |
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> the developer had to sacrifice your ability to predict what a device name will |
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> be. |
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> |
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> You actually don't care what the name of a thing in /dev/ is, it really |
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> doesn't matter. The kernel knows what they are by looking at the major and |
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> minor numbers and the name only exists while that instance of udev is running. |
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> To work with the device (eg mounting it), you should use some other |
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> characteristic of the device, like it's serial number or volume label. Which |
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> means things like /dev/sda3 should not appear in fstab. |
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> |
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> View it this way: |
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> |
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> You have a disk volume with a filesystem on it that you called "HOME", and you |
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> want to mount that filesystem to /home. You should just do that directly. |
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> |
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> The other way involves a completely useless extra step that the user doe snot |
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> even need to know about: You have a filesystem on it called "HOME", so you |
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> looked it up in some arcane table and found that it has the arbitrary name of |
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> /dev/sda3, so you mount /dev/sda3 to /home. Hmmmmmm, what's this extra step of |
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> looking something up somewhere? It serves no useful purpose, gives no extra |
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> information and is completely redundant. |
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> |
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> If all you are doing is making filesystems available for use, and you find you |
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> are getting involved with device names, then you are doing something contrary |
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> to current kernel/udev/userspace practice. |
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|
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If your last paragraph ist true, then it is probably time |
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to rewrite Gentoo Handbook. I just checked it, especially |
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section 4 "Preparing the Disks" and 8 "Configuring your System" |
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and did not find a word about udev, and this new concept of |
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device files (maybe time to file bug concerning Gentoo doc?). |
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|
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In Gentoo Handbook, device files are still used in fstab. |
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And what's even worse, there is no warning about what just |
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happened to me: user can have perfectly working system, |
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which he installed/configured using Gentoo Handbook. |
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Then he just adds one more hard-drive, and this renders |
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his system completely unusable, just because sudenly fstab |
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does not match with new dev-file names... |
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For me this is the 2nd day I've lost by reading about udev, |
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trying figure out how to make my system "udev-proof". |
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That's too much cost for just adding new hard-disk... |
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|
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Jarry |
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-- |
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