On 16 November 2011 14:54, Bryan J Smith <b.j.sm...@ieee.org> wrote: > I thought "df" just reads superblock information, as inode file systems > store free blocks and inode counts (and FAT file systems have similar > structures)? This came up on LinkedIn last week IIRC, and after the same > comment, I verified with strace that df was calling statfs64 with > "[MAGIC_]SUPER" constants. > > Did you mean "du" with regards to dentry/lstat? > > > -- Bryan > > P.S. As far as scripting, the strace (or the source code of df for that > matter) will also give you many of the calls "df" actually makes to get > this information from the superblock. > > > I wondered how df found the mount point for "df <dir>" and I found it called lstat() several times, presumably to find a match against the entry in /etc/mtab. I didn't dig into the code to find out exactly what it was doing. The call for the actual disk space is still statfs().
I've had a few goes at getting disk space for various things over the years: df itself does hang sometimes, statfs() can do, but is sometimes less problematic and quicker. df -P <dir> is probably the simplest start, if it gives problems you can always try something else. jch
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