Imagine people want to install Gentoo via a CD-ROM or USB flash disk connected through USB. Or, which was my case right now, want to install Gentoo on USB flash disk. It takes a while before usb-storage probes for scsi disk device. In my case, init too quickly tries to mount root filesystem (in my case located on the USB flash drive). Because it cannot mount it, it panics. User cannot scroll up/down because the console is locked. First, adding the mount delay gives first of all the user time to scroll through the screen buffer up&down to see e.g. which drivers picked up some devices or not. I could only otherwise think of attaching a remote serial console to catch the output. Second, the USB drive gets recognized in my case within 5 seconds but I believe the delay is not harmful. I believe it is safe to add these two parameters to the kernel command-line.
Created attachment 151384 [details] dmesg-2.6.24-gentoo-r4-default.txt
The important part of the dmesg output is here: Waiting 15sec before mounting root device... scsi 6:0:0:0: Direct-Access PQ: 0 ANSI: 2 CCS sd 6:0:0:0: [sde] Attached SCSI disk sd 6:0:0:0: Attached scsi generic sg4 type 0 usb-storage: device scan complete scsi 7:0:0:0: Direct-Access USB 2.0 Flash Disk 0.00 PQ: 0 ANSI: 2 sd 7:0:0:0: [sdf] 7897087 512-byte hardware sectors (4043 MB) sd 7:0:0:0: [sdf] Write Protect is off sd 7:0:0:0: [sdf] Mode Sense: 00 00 00 00 sd 7:0:0:0: [sdf] Assuming drive cache: write through sd 7:0:0:0: [sdf] 7897087 512-byte hardware sectors (4043 MB) sd 7:0:0:0: [sdf] Write Protect is off sd 7:0:0:0: [sdf] Mode Sense: 00 00 00 00 sd 7:0:0:0: [sdf] Assuming drive cache: write through sdf: sdf1 sd 7:0:0:0: [sdf] Attached SCSI removable disk sd 7:0:0:0: Attached scsi generic sg5 type 0 usb-storage: device scan complete md: Autodetecting RAID arrays. md: Scanned 0 and added 0 devices. md: autorun ... md: ... autorun DONE. VFS: Mounted root (ext2 filesystem) readonly.
We already document the slowusb command. We do not want to introduce a *forced* delay on all users, given that USB-booting users are going to be a vast minority. As such, I'm marking this as WONTFIX.
Maybe I should say it more clearly. I believe slowusb does not make them waiting for a long time, it appears to me kernel or the usb-driver decides itself. The rootdelay=15 is another story. How about about providing a safe/rescue grub entry on distribution media where these would be involved? The rootdelay= is especially usefull because when the kernel cannot mount root filesystem (the installation CDROM) the kernel panics. and user has no way to scroll back the screen. By using this option he/she has 15 seconds. ;-) Alternatively, the kernel can wait forever, so it would not introduce the delay to anybody as long as the root filesystem path was specified correctly. rootwait [KNL] Wait (indefinitely) for root device to show up. Useful for devices that are detected asynchronously (e.g. USB and MMC devices). Still, I believe slowusb is safe.
I am not sure that you understand the meaning of WONTFIX. It means that we are not interested in making these changes. I explained previously why we do not want to make these changes to our media and marked the bug accordingly. Please, do not reopen this bug, as my opinion on this isn't going to change.
