core: Reduce amount of calls to getattr/Stat, improve vfs.read #157
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For many operations, we currently call VirtualFileSystem#getattr(Inode), which gets a full set of "stat" metadata for a given Inode. In many cases however, we're only interested in the type of the Inode (e.g., directory, regular file, symlink, etc.). Certain VirtualFileSystem implementations may be able to retrieve that specific information significantly faster than the full metadata set. Replace calls to vfs.getattr(Inode).type() with vfs.getStatType() where applicable, and provide default implementations for backwards compatibility. Also don't retrieve Stat information at all where not required: 1. In PseudoFS.checkAccess with ACE4_READ_ATTRIBUTES, and 2. For OperationREAD, allow VirtualFileSystem to skip the Stat check (currently checking StatType but also file size), which is currently done per every call to "read": Clarify the requirement of signaling "eof reached" as per NFSv4 spec, provide a new read() method to VirtualFileSystem with a corresponding callback function, and provide a default implementation for backwards compatibility. Signed-off-by: Christian Kohlschütter <[email protected]>
Signed-off-by: Christian Kohlschütter <[email protected]>
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Are there any benchmarks that justify this change? Almost all operations are subject to permission checks, thus, file attributes are almost always required. To reduce the number of filesystem calls, we use VfsCache which aggressively caches getattrs. |
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The file type can (in many cases) be encoded directly in the Inode file handle, which means that the lookup is free. Caching can only go so far, especially when the file can be modified outside of nfs4j. |
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For many operations, we currently call VirtualFileSystem#getattr(Inode), which gets a full set of "stat" metadata for a given Inode.
In many cases however, we're only interested in the type of the Inode (e.g., directory, regular file, symlink, etc.). Certain VirtualFileSystem implementations may be able to retrieve that specific information significantly faster than the full metadata set.
Replace calls to vfs.getattr(Inode).type() with vfs.getStatType() where applicable, and provide default implementations for backwards compatibility.
Also don't retrieve Stat information at all where not required:
In PseudoFS.checkAccess with ACE4_READ_ATTRIBUTES, and
For OperationREAD, allow VirtualFileSystem to skip the Stat check (currently checking StatType but also file size), which is currently done per every call to "read":
Clarify the requirement of signaling "eof reached" as per NFSv4 spec, provide a new read() method to VirtualFileSystem with a corresponding callback function, and provide a default implementation for backwards compatibility.