Hi Peng,
For file/dir deletion, we remove the corresponding directory entry first
to guarantee that the object is no longer visible, then we begin tearing
down whatever objects are left (metadata, datafiles, etc.).
For rename we first create the new directory entry, then remove the old
directory entry (so there is a window of time where the object has two
"names", but may be correctly accessed under either), then remove
anything that used to be referred to by the new name.
Block allocation is handled by the underlying local file systems; we
don't have to do anything there.
Generally you can figure this sort of stuff out by looking at the state
machine state names; they're fairly descriptive.
Rob
Peng Gu wrote:
I am studying the way PVFS2 takes to keep its filesystem consistency.
For example, pvfs2-guide tell us the steps for PVFS2 to create a file
on webpage http://www.pvfs.org/pvfs2-guide.html#SECTION00036000000000000000
Here is some sentences cited from that page:
"Here are the steps necessary to create a new file in PVFS2:
create a directory entry for the new file
create a metadata object for the new file
point the directory entry to the metadata object
create a set of data objects to hold data for the new file
point the metadata at the data objects
Performing those steps in that particular order results in file system
states where a directory entry exists for a file that is not really
ready to be accessed. If we carefully order the operations:
1. create the data objects to hold data for the new file
2. create a metadata object for the new file
3. point the metadata at the data objects
4. create a directory entry for the new file pointing to the metadata
object
we create a sequence of states that always leave the file system
directory hierarchy in a consistent state. The file is either there
(and ready to be accessed) or it isn't. All PVFS2 operations are
performed in this manner."
Can anybody tell me the steps PVFS2 takes for other operations like
file/dir deletion, file renaming, free space/block allocation/release.
Thanks,
Peng
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