Date: Sat, 24 May 2014 17:41:02 +0200 From: Polytropon <freebsd@edvax.de> To: Arthur Chance <freebsd@qeng-ho.org> Cc: FreeBSD Mailing List <freebsd-questions@freebsd.org> Subject: Re: write-protected usb flash drive Message-ID: <20140524174102.66eff3da.freebsd@edvax.de> In-Reply-To: <5380B953.5090700@qeng-ho.org> References: <537FE744.3030002@dreamchaser.org> <20140524080127.f2e788d5.freebsd@edvax.de> <5380AB17.2070300@dreamchaser.org> <5380B953.5090700@qeng-ho.org>
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On Sat, 24 May 2014 16:22:59 +0100, Arthur Chance wrote: > OK, thought I'd better try my own advice rather than just handing it > out. I put a microSD card out of an old phone into a SanDisk mSD -> SD > adapter and plugged that into my SanDisk SD -> USB adapter, mounted it > (FAT32 file system already on it) and wrote a file to it. Worked as > you'd expect. I then unmounted and unplugged it, flipped the write > protect switch and tried to remount. Result was > > mount_msdosfs: /dev/da5s1: Input/output error > > Mounting it read-only was fine. So, the write protect is honoured by at > least some SD -> USB adapters. This is already on file system level. It _should_ work the same at upper layers, for example when using dd to write NULs to the device with the write protection on - an error should (correctly) occur in that case. When a r/o mount is forced, the routines accessing that file system cannot avoid the write protection. Still writes are possible _aside of_ the file system which should be prevented by the switch as well. It's probably a good idea to check that too, e. g. put in the card with write protection on and then try dd or newfs on it. -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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