Messages in this thread | | | Date | Wed, 7 Apr 2004 11:21:40 -0500 (CDT) | From | Bruce Allen <> | Subject | Re: dd PATCH: add conv=direct |
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> > On modern Linux, apparently the correct way to bypass the buffer cache > > when writing to a block device is to open the block device with > > O_DIRECT. This enables, for example, the user to more easily force a > > reallocation of a single sector of an IDE disk with a media error > > (without overwriting anything but the 1k "sector pair" containing the > > error). dd(1) is convenient for this purpose, but is lacking a method > > to force O_DIRECT. The enclosed patch adds a "conv=direct" flag to > > enable this usage. > > This would be rather nice to have. You'll need to ensure that the data > is page-aligned in memory. > > While you're there, please add an fsync-before-closing option.
Andrew, am I right that this is NOT needed for the proposed O_DIRECT option, since open(2) says: "The I/O is synchronous, i.e., at the completion of the read(2) or write(2) system call, data is guaranteed to have been transferred." so the write will block until data is physically on the disk.
Cheers, Bruce
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