aboutsummaryrefslogtreecommitdiff
path: root/Documentation/usb/mass-storage.rst
diff options
context:
space:
mode:
authorLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
committerLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
commit5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch)
treecc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/usb/mass-storage.rst
downloadlinux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.tar.gz
linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.zip
Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted
Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ...
Diffstat (limited to '')
-rw-r--r--Documentation/usb/mass-storage.rst243
1 files changed, 243 insertions, 0 deletions
diff --git a/Documentation/usb/mass-storage.rst b/Documentation/usb/mass-storage.rst
new file mode 100644
index 000000000..f399ec631
--- /dev/null
+++ b/Documentation/usb/mass-storage.rst
@@ -0,0 +1,243 @@
+=========================
+Mass Storage Gadget (MSG)
+=========================
+
+Overview
+========
+
+ Mass Storage Gadget (or MSG) acts as a USB Mass Storage device,
+ appearing to the host as a disk or a CD-ROM drive. It supports
+ multiple logical units (LUNs). Backing storage for each LUN is
+ provided by a regular file or a block device, access can be limited
+ to read-only, and gadget can indicate that it is removable and/or
+ CD-ROM (the latter implies read-only access).
+
+ Its requirements are modest; only a bulk-in and a bulk-out endpoint
+ are needed. The memory requirement amounts to two 16K buffers.
+ Support is included for full-speed, high-speed and SuperSpeed
+ operation.
+
+ Note that the driver is slightly non-portable in that it assumes
+ a single memory/DMA buffer will be usable for bulk-in and bulk-out
+ endpoints. With most device controllers this is not an issue, but
+ there may be some with hardware restrictions that prevent a buffer
+ from being used by more than one endpoint.
+
+ This document describes how to use the gadget from user space, its
+ relation to mass storage function (or MSF) and different gadgets
+ using it, and how it differs from File Storage Gadget (or FSG)
+ (which is no longer included in Linux). It will talk only briefly
+ about how to use MSF within composite gadgets.
+
+Module parameters
+=================
+
+ The mass storage gadget accepts the following mass storage specific
+ module parameters:
+
+ - file=filename[,filename...]
+
+ This parameter lists paths to files or block devices used for
+ backing storage for each logical unit. There may be at most
+ FSG_MAX_LUNS (8) LUNs set. If more files are specified, they will
+ be silently ignored. See also “luns” parameter.
+
+ *BEWARE* that if a file is used as a backing storage, it may not
+ be modified by any other process. This is because the host
+ assumes the data does not change without its knowledge. It may be
+ read, but (if the logical unit is writable) due to buffering on
+ the host side, the contents are not well defined.
+
+ The size of the logical unit will be rounded down to a full
+ logical block. The logical block size is 2048 bytes for LUNs
+ simulating CD-ROM, block size of the device if the backing file is
+ a block device, or 512 bytes otherwise.
+
+ - removable=b[,b...]
+
+ This parameter specifies whether each logical unit should be
+ removable. “b” here is either “y”, “Y” or “1” for true or “n”,
+ “N” or “0” for false.
+
+ If this option is set for a logical unit, gadget will accept an
+ “eject” SCSI request (Start/Stop Unit). When it is sent, the
+ backing file will be closed to simulate ejection and the logical
+ unit will not be mountable by the host until a new backing file is
+ specified by userspace on the device (see “sysfs entries”
+ section).
+
+ If a logical unit is not removable (the default), a backing file
+ must be specified for it with the “file” parameter as the module
+ is loaded. The same applies if the module is built in, no
+ exceptions.
+
+ The default value of the flag is false, *HOWEVER* it used to be
+ true. This has been changed to better match File Storage Gadget
+ and because it seems like a saner default after all. Thus to
+ maintain compatibility with older kernels, it's best to specify
+ the default values. Also, if one relied on old default, explicit
+ “n” needs to be specified now.
+
+ Note that “removable” means the logical unit's media can be
+ ejected or removed (as is true for a CD-ROM drive or a card
+ reader). It does *not* mean that the entire gadget can be
+ unplugged from the host; the proper term for that is
+ “hot-unpluggable”.
+
+ - cdrom=b[,b...]
+
+ This parameter specifies whether each logical unit should simulate
+ CD-ROM. The default is false.
+
+ - ro=b[,b...]
+
+ This parameter specifies whether each logical unit should be
+ reported as read only. This will prevent host from modifying the
+ backing files.
+
+ Note that if this flag for given logical unit is false but the
+ backing file could not be opened in read/write mode, the gadget
+ will fall back to read only mode anyway.
+
+ The default value for non-CD-ROM logical units is false; for
+ logical units simulating CD-ROM it is forced to true.
+
+ - nofua=b[,b...]
+
+ This parameter specifies whether FUA flag should be ignored in SCSI
+ Write10 and Write12 commands sent to given logical units.
+
+ MS Windows mounts removable storage in “Removal optimised mode” by
+ default. All the writes to the media are synchronous, which is
+ achieved by setting the FUA (Force Unit Access) bit in SCSI
+ Write(10,12) commands. This forces each write to wait until the
+ data has actually been written out and prevents I/O requests
+ aggregation in block layer dramatically decreasing performance.
+
+ Note that this may mean that if the device is powered from USB and
+ the user unplugs the device without unmounting it first (which at
+ least some Windows users do), the data may be lost.
+
+ The default value is false.
+
+ - luns=N
+
+ This parameter specifies number of logical units the gadget will
+ have. It is limited by FSG_MAX_LUNS (8) and higher value will be
+ capped.
+
+ If this parameter is provided, and the number of files specified
+ in “file” argument is greater then the value of “luns”, all excess
+ files will be ignored.
+
+ If this parameter is not present, the number of logical units will
+ be deduced from the number of files specified in the “file”
+ parameter. If the file parameter is missing as well, one is
+ assumed.
+
+ - stall=b
+
+ Specifies whether the gadget is allowed to halt bulk endpoints.
+ The default is determined according to the type of USB device
+ controller, but usually true.
+
+ In addition to the above, the gadget also accepts the following
+ parameters defined by the composite framework (they are common to
+ all composite gadgets so just a quick listing):
+
+ - idVendor -- USB Vendor ID (16 bit integer)
+ - idProduct -- USB Product ID (16 bit integer)
+ - bcdDevice -- USB Device version (BCD) (16 bit integer)
+ - iManufacturer -- USB Manufacturer string (string)
+ - iProduct -- USB Product string (string)
+ - iSerialNumber -- SerialNumber string (sting)
+
+sysfs entries
+=============
+
+ For each logical unit, the gadget creates a directory in the sysfs
+ hierarchy. Inside of it the following three files are created:
+
+ - file
+
+ When read it returns the path to the backing file for the given
+ logical unit. If there is no backing file (possible only if the
+ logical unit is removable), the content is empty.
+
+ When written into, it changes the backing file for given logical
+ unit. This change can be performed even if given logical unit is
+ not specified as removable (but that may look strange to the
+ host). It may fail, however, if host disallowed medium removal
+ with the Prevent-Allow Medium Removal SCSI command.
+
+ - ro
+
+ Reflects the state of ro flag for the given logical unit. It can
+ be read any time, and written to when there is no backing file
+ open for given logical unit.
+
+ - nofua
+
+ Reflects the state of nofua flag for given logical unit. It can
+ be read and written.
+
+ - forced_eject
+
+ When written into, it causes the backing file to be forcibly
+ detached from the LUN, regardless of whether the host has allowed
+ it. The content doesn't matter, any non-zero number of bytes
+ written will result in ejection.
+
+ Can not be read.
+
+ Other then those, as usual, the values of module parameters can be
+ read from /sys/module/g_mass_storage/parameters/* files.
+
+Other gadgets using mass storage function
+=========================================
+
+ The Mass Storage Gadget uses the Mass Storage Function to handle
+ mass storage protocol. As a composite function, MSF may be used by
+ other gadgets as well (eg. g_multi and acm_ms).
+
+ All of the information in previous sections are valid for other
+ gadgets using MSF, except that support for mass storage related
+ module parameters may be missing, or the parameters may have
+ a prefix. To figure out whether any of this is true one needs to
+ consult the gadget's documentation or its source code.
+
+ For examples of how to include mass storage function in gadgets, one
+ may take a look at mass_storage.c, acm_ms.c and multi.c (sorted by
+ complexity).
+
+Relation to file storage gadget
+===============================
+
+ The Mass Storage Function and thus the Mass Storage Gadget has been
+ based on the File Storage Gadget. The difference between the two is
+ that MSG is a composite gadget (ie. uses the composite framework)
+ while file storage gadget was a traditional gadget. From userspace
+ point of view this distinction does not really matter, but from
+ kernel hacker's point of view, this means that (i) MSG does not
+ duplicate code needed for handling basic USB protocol commands and
+ (ii) MSF can be used in any other composite gadget.
+
+ Because of that, File Storage Gadget has been removed in Linux 3.8.
+ All users need to transition to the Mass Storage Gadget. The two
+ gadgets behave mostly the same from the outside except:
+
+ 1. In FSG the “removable” and “cdrom” module parameters set the flag
+ for all logical units whereas in MSG they accept a list of y/n
+ values for each logical unit. If one uses only a single logical
+ unit this does not matter, but if there are more, the y/n value
+ needs to be repeated for each logical unit.
+
+ 2. FSG's “serial”, “vendor”, “product” and “release” module
+ parameters are handled in MSG by the composite layer's parameters
+ named respectively: “iSerialnumber”, “idVendor”, “idProduct” and
+ “bcdDevice”.
+
+ 3. MSG does not support FSG's test mode, thus “transport”,
+ “protocol” and “buflen” FSG's module parameters are not
+ supported. MSG always uses SCSI protocol with bulk only
+ transport mode and 16 KiB buffers.