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Message-ID: <20070226214215.GE10715@schatzie.adilger.int> Date: Mon, 26 Feb 2007 14:42:15 -0700 From: Andreas Dilger <adilger@...sterfs.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Kalpak Shah <kalpak@...sterfs.com>, linux-ext4@...r.kernel.org, tytso@....edu, sct@...hat.com Subject: Re: [RFC] [PATCH 1/1] nanosecond timestamps On Feb 25, 2007 02:36 -0800, Andrew Morton wrote: > > On Fri, 02 Feb 2007 20:09:40 +0530 Kalpak Shah <kalpak@...sterfs.com> wrote: > > +#define EXT3_INODE_GET_XTIME(xtime, extra_xtime, inode, raw_inode) > > \ > > +do { > > \ > > + (inode)->xtime.tv_sec = le32_to_cpu((raw_inode)->xtime); > > \ > > + \ > > + if (offsetof(typeof(*raw_inode), extra_xtime) - > > \ > > + offsetof(typeof(*raw_inode), i_extra_isize) + > > \ > > + sizeof((raw_inode)->extra_xtime) <= > > \ > > + le16_to_cpu((raw_inode)->i_extra_isize)) { > > \ > > + if (sizeof((inode)->xtime.tv_sec) > 4) \ > > + (inode)->xtime.tv_sec |= \ > > + (__u64)(le32_to_cpu((raw_inode)->extra_xtime) & \ > > + EXT3_EPOCH_MASK) << 32; \ > > + (inode)->xtime.tv_nsec = \ > > + (le32_to_cpu((raw_inode)->extra_xtime) & \ > > + EXT3_NSEC_MASK) >> 2; \ > > + } > > \ > > +} while (0) > > ow, my eyes. Can we find a way to do this in C rather than in cpp? The macro is working on the field names of the inode in most places (e.g. i_mtime, i_ctime, etc) rather than the values. You _could_ do it in C, but it would mean moving all of the "offsetof()" into the caller (basically putting the whole macro in-line at the caller) or doing math on the pointer addresses at runtime instead of compile time. It boils down to a check whether the particular nanosecond field is inside the reserved space in the inode or not, so it ends up a comparison against a constant. For ctime: if (4 <= le32_to_cpu((raw_inode)->i_extra_isize) { And the second "if" decides whether to save bits > 32 in the seconds field for 64-bit architectures, so it is also evaluated at compile time. Better to have this in a macro than in the code itself. Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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