From 3448914e8cc550ba792d4ccc74471d1ca4293aae Mon Sep 17 00:00:00 2001 From: Martijn Coenen Date: Wed, 13 May 2020 15:38:45 +0200 Subject: loop: Add LOOP_CONFIGURE ioctl This allows userspace to completely setup a loop device with a single ioctl, removing the in-between state where the device can be partially configured - eg the loop device has a backing file associated with it, but is reading from the wrong offset. Besides removing the intermediate state, another big benefit of this ioctl is that LOOP_SET_STATUS can be slow; the main reason for this slowness is that LOOP_SET_STATUS(64) calls blk_mq_freeze_queue() to freeze the associated queue; this requires waiting for RCU synchronization, which I've measured can take about 15-20ms on this device on average. In addition to doing what LOOP_SET_STATUS can do, LOOP_CONFIGURE can also be used to: - Set the correct block size immediately by setting loop_config.block_size (avoids LOOP_SET_BLOCK_SIZE) - Explicitly request direct I/O mode by setting LO_FLAGS_DIRECT_IO in loop_config.info.lo_flags (avoids LOOP_SET_DIRECT_IO) - Explicitly request read-only mode by setting LO_FLAGS_READ_ONLY in loop_config.info.lo_flags Here's setting up ~70 regular loop devices with an offset on an x86 Android device, using LOOP_SET_FD and LOOP_SET_STATUS: vsoc_x86:/system/apex # time for i in `seq 30 100`; do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done 0m03.40s real 0m00.02s user 0m00.03s system Here's configuring ~70 devices in the same way, but using a modified losetup that uses the new LOOP_CONFIGURE ioctl: vsoc_x86:/system/apex # time for i in `seq 30 100`; do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done 0m01.94s real 0m00.01s user 0m00.01s system Signed-off-by: Martijn Coenen Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- include/uapi/linux/loop.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'include/uapi/linux/loop.h') diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h index 6b32fee80ce0..24a1c45bd1ae 100644 --- a/include/uapi/linux/loop.h +++ b/include/uapi/linux/loop.h @@ -31,6 +31,10 @@ enum { /* LO_FLAGS that can be cleared using LOOP_SET_STATUS(64) */ #define LOOP_SET_STATUS_CLEARABLE_FLAGS (LO_FLAGS_AUTOCLEAR) +/* LO_FLAGS that can be set using LOOP_CONFIGURE */ +#define LOOP_CONFIGURE_SETTABLE_FLAGS (LO_FLAGS_READ_ONLY | LO_FLAGS_AUTOCLEAR \ + | LO_FLAGS_PARTSCAN | LO_FLAGS_DIRECT_IO) + #include /* for __kernel_old_dev_t */ #include /* for __u64 */ @@ -66,6 +70,22 @@ struct loop_info64 { __u64 lo_init[2]; }; +/** + * struct loop_config - Complete configuration for a loop device. + * @fd: fd of the file to be used as a backing file for the loop device. + * @block_size: block size to use; ignored if 0. + * @info: struct loop_info64 to configure the loop device with. + * + * This structure is used with the LOOP_CONFIGURE ioctl, and can be used to + * atomically setup and configure all loop device parameters at once. + */ +struct loop_config { + __u32 fd; + __u32 block_size; + struct loop_info64 info; + __u64 __reserved[8]; +}; + /* * Loop filter types */ @@ -96,6 +116,7 @@ struct loop_info64 { #define LOOP_SET_CAPACITY 0x4C07 #define LOOP_SET_DIRECT_IO 0x4C08 #define LOOP_SET_BLOCK_SIZE 0x4C09 +#define LOOP_CONFIGURE 0x4C0A /* /dev/loop-control interface */ #define LOOP_CTL_ADD 0x4C80 -- cgit v1.2.3