I've just purchased a TP-Link wireless access point. Despite owning the thing, the model of the item remains somewhat unclear: it's variously known as the "TL-WDR7500," "AC1750," and the "Archer C7." Fortunately, what was clear is that it has good specs (including immensely more memory than the WRT54Gs I've been playing with, and two USB2 ports), it's very well supported by OpenWRT (mine is the one with three antennas). This is a version 2, which is also good as that has more memory than version 1.x. And installing OpenWRT was literally as easy as downloading barrier_breaker/14.07/ar71xx/generic/openwrt-ar71xx-generic-archer-c7-v2-squashfs-factory.bin, logging in to the router's admin interface and then to "Firmware Upgrade," pointing to the downloaded file, and pressing the "Upgrade" button. It doesn't get much simpler than that.
[What follows is for the Barrier Breaker version of OpenWRT: to read more about the same process for the CC version, see Mounting a USB Drive on OpenWRT Chaos Calmer.]
Getting OpenWRT to talk to the two USB ports on the device was unpleasantly difficult. With the default install, dmesg made it clear that the insertion of a USB device was duly noted with a log entry like this:
usb 2-1: new high-speed USB device number 3 using ehci-platform
but there was no further information - perhaps noting whether or not it was a drive rather than a mouse? Or what device number it was. I started to work through the information at http://wiki.openwrt.org/doc/howto/usb.storage . So I installed:
kmod-usb-storage kmod-scsi-core
which you'd think would be in the default squashfs file for this specific device as they'd already included kmod-usb-core. I kind of understand why they didn't include the filesystem types (who knows which you're going to need?) so I installed:
kmod-fs-msdos kmod-fs-vfat
It was possible to do insmod kmod-usb-storage and insmod kmod-fs-vfat after these installs, but I found behaviour was better after a reboot: I have to assume there's scripts and autodetection that set these up better than a naked insmod command. Still, it's a bit annoying to have to reboot a Linux device as if it were Windows ...
And finally I installed:
block-mount
which is apparently required to mount any device. Again, shouldn't that be in the default image?
At this point, dmesg was acknowledging that we have genuine USB storage devices attached:
usb 1-1: new high-speed USB device number 2 using ehci-platform usb-storage 1-1:1.0: USB Mass Storage device detected scsi0 : usb-storage 1-1:1.0 scsi 0:0:0:0: Direct-Access USB 3.0 USB Flash Drive 1.00 PQ: 0 ANSI: 6 sd 0:0:0:0: [sda] 30883840 512-byte logical blocks: (15.8 GB/14.7 GiB) sd 0:0:0:0: [sda] Write Protect is off sd 0:0:0:0: [sda] Mode Sense: 23 00 00 00 sd 0:0:0:0: [sda] Write cache: disabled, read cache: disabled, doesn't support DPO or FUA sda: sda1 sd 0:0:0:0: [sda] Attached SCSI removable disk
But attempting to run mount /dev/sda1 /mnt/ fails with mount: mounting /dev/sda1 on /mnt/ failed: Invalid argument, although we do now have a /dev/sda1 device in the /dev/ folder and /mnt/ is a valid folder.
After hours of tests and googling, I finally stumbled across an obscure hint from someone who was asking another question but had "solved the USB problem" ... they had installed the appropriate NLS ("Native Language Support") packages for their area. Seriously? But I'm willing to try anything by this point, so I installed:
kmod-nls-iso8859-1 kmod-nls-cp437
Test again, and ... I can mount USB storage devices! At least ones with a filesystem that I've installed, so I guess I need to install NTFS and/or ext3/4 support if I want to use hard drives.
This solution is both non-obvious and not well documented. I see in looking back at the OpenWRT documentation that they DO mention the NLS packages. But I didn't notice at the time and they weren't dependencies enforced by the package manager, so they got lost. <sigh>
Update: I've confirmed that the NLS packages are needed for vfat file systems and not needed for ext4 and iso9660 file systems. And of course which NLS file(s) are appropriate to you are going to vary with your language, so making it a dependency is very difficult.