Messages in this thread | | | From | Jeff Moyer <> | Date | Tue, 24 Jan 2006 07:09:08 -0500 | Subject | Re: [patch] fix O_DIRECT read of last block in a sparse file |
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==> Regarding Re: [patch] fix O_DIRECT read of last block in a sparse file; Andrew Morton <akpm@osdl.org> adds:
akpm> Jeff Moyer <jmoyer@redhat.com> wrote: >> Currently, if you open a file O_DIRECT, truncate it to a size that is >> not a multiple of the disk block size, and then try to read the last >> block in the file, the read will return 0. The problem is in >> do_direct_IO, here: >> >> /* Handle holes */ if (!buffer_mapped(map_bh)) { char *kaddr; >> >> ... >> >> if (dio->block_in_file >= i_size_read(dio->inode)>>blkbits) { /* We hit >> eof */ page_cache_release(page); goto out; } >> >> We shift off any remaining bytes in the final block of the I/O, >> resulting in a 0-sized read. I've attached a patch that fixes this. >> I'm not happy about how ugly the math is getting, so suggestions are >> more than welcome. >> >> I've tested this with a simple program that performs the steps outlined >> for reproducing the problem above. Without the patch, we get a 0-sized >> result from read. With the patch, we get the correct return value from >> the short read.
akpm> OK. We do have some helper functions to make the math a little akpm> clearer. How does this look?
That's much cleaner, thanks!
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