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@@ -155,7 +155,7 @@
unnamed temporary file on that filesystem
- As with tmpfile(), the file disppears on
+ As with tmpfile(), the file disappears on
last close()
@@ -170,27 +170,6 @@
-
-
Lustre filesystem [3.12]
-
-
- A distributed filesystem, popular for cluster computing
- applications
-
-
- Developed out-of-tree since 1999, but now added to Linux staging
- directory
-
-
- Was included in squeeze but dropped from wheezy as it didn't
- support Linux 3.2
-
-
- Userland is now missing from Debian
-
-
-
-
Network busy-polling [3.11] (1)
A conventional network request/response process looks like:
@@ -253,13 +232,37 @@
+
+
Lustre filesystem [3.12]
+
+
+ A distributed filesystem, popular for cluster computing
+ applications
+
+
+ Developed out-of-tree since 1999, but now added to Linux staging
+ directory
+
+
+ Was included in squeeze but dropped from wheezy as it didn't
+ support Linux 3.2
+
+
+ Userland is now missing from Debian
+
+
+
+
Btrfs offline dedupe [3.12]
- Btrfs generally does COW rather than updating in-place, allowing
- snapshots and file copies to defer the actual copying and save
- space
+ Btrfs generally copies and frees blocks, rather than updating
+ in-place
+
+
+ This allows snapshots and file copies to copy-by-reference,
+ deferring the real copying until changes are made
Filesystems may still end up with multiple copies of the same
@@ -276,6 +279,135 @@
+
+
nftables [3.13]
+
+
+ Linux has several firewall APIs - iptables, ip6tables, arptables
+ and ebtables
+
+
+ All limited to single protocol, and need a kernel module for
+ each match type and each action
+
+
+ Kernel's internal netfilter API is more flexible
+
+
+ nftables exposes more of this flexibility, allowing userland
+ to provide firewall code for a specialised VM (similar to BPF)
+
+
+ nftables userland tool uses this API and is already packaged
+
+
+ Eventually, old APIs will be removed and old userland
+ tools must be ported to use nftables
+
+
+
+
+
+
User-space lockdep [3.14]
+
+
+ Kernel threads and interrupts all run in same address space,
+ using several different synchronisation mechanisms
+
+
+ Easy to introduce bugs that can result in deadlock, but hard to
+ reproduce them
+
+
+ Kernel's 'lockdep' system dynamically tracks locking operations
+ and detects potential deadlocks
+
+
+ Now available as a userland library! Except we need to package
+ it (build from linux-tools source package)
+
+
+
+
+
+
arm64 and ppc64el ports
+
+
+ 'arm64' architecture was added in Linux 3.7, but was not yet
+ usable, and no real hardware was available at the time
+
+
+ Upstream Linux arm64 kernel, and Debian packages, should now run
+ on emulators and real hardware
+
+
+ 'powerpc' architecture has been available for many years,
+ but didn't support kernel running little-endian
+
+
+ Linux 3.13 added little-endian kernel support, along with new
+ userland ELF ABI variant - we call it ppc64el
+
+
+ Both ports now being bootstrapped in unstable and are candidates
+ for jessie release
+
+
+
+
+
+
File-private locking [3.15]
+
+
+ POSIX says that closing a file descriptor removes
+ the process's locks on that file
+
+
+ What if process has multiple file descriptors for the same
+ file? It loses all locks obtained through any descriptor!
+
+
+ Multithreaded processes may require serialisation around
+ file open/close to ensure they open each file exactly once
+
+
+ Hard and symbolic links can hide that two files are really the
+ same
+
+
+ Linux now provides file-private locks, associated with a
+ specific open file and removed when last descriptor for the
+ open file is closed
+
+
+
+
+
+
Multiqueue block devices [3.16]
+
+
+ Each block device has a command queue (possibly shared with
+ other devices)
+
+
+ Queue may be partly implemented by hardware (NCQ) or only
+ in software
+
+
+ A single queue means initiation is serialised and completion
+ involves IPI - can be bottleneck for fast devices
+
+
+ High-end SSDs support multiple queues, but kernel needed changes
+ to use them
+
+
+ mtip32xx driver now supports multiqueue, but SCSI
+ drivers don't yet - may be backport-able?
+