45734a235
Denys Vlasenko
2022-12-13
Subject
loop: optionally use ioctl(LOOP_CONFIGURE) to set up loopdevs
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libbb/Config.src+22 -0
| @@ -369,3 +369,25 @@ config UNICODE_PRESERVE_BROKEN | |
| For example, this means that entering 'l', 's', ' ', 0xff, [Enter] | |
| at shell prompt will list file named 0xff (single char name | |
| with char value 255), not file named '?'. | |
| + | |
| + | choice |
| + | prompt "Use LOOP_CONFIGURE for losetup and loop mounts" |
| + | default TRY_LOOP_CONFIGURE |
| + | help |
| + | LOOP_CONFIGURE is added to Linux 5.8 |
| + | https://lwn.net/Articles/820408/ |
| + | 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. |
| + | |
| + | config LOOP_CONFIGURE |
| + | bool "use LOOP_CONFIGURE, needs kernel >= 5.8" |
| + | |
| + | config NO_LOOP_CONFIGURE |
| + | bool "use LOOP_SET_FD + LOOP_SET_STATUS" |
| + | |
| + | config TRY_LOOP_CONFIGURE |
| + | bool "try LOOP_CONFIGURE, fall back to LOOP_SET_FD + LOOP_SET_STATUS" |
| + | |
| + | endchoice |
libbb/loop.c+43 -9
| @@ -110,26 +110,39 @@ static int get_next_free_loop(char *dev, int id) | |
| return loopdevno; | |
| } | |
| - | static int set_loopdev_params(int ffd, |
| - | int lfd, const char *file, |
| + | #if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE |
| + | # define LOOP_CONFIGURE 0x4C0A |
| + | struct loop_config { |
| + | uint32_t fd; |
| + | uint32_t block_size; |
| + | struct loop_info64 info; |
| + | uint64_t __reserved[8]; |
| + | }; |
| + | #endif |
| + | |
| + | static int set_loopdev_params(int lfd, |
| + | int ffd, const char *file, |
| unsigned long long offset, | |
| unsigned long long sizelimit, | |
| unsigned flags) | |
| { | |
| int rc; | |
| + | #if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE |
| + | struct loop_config lconfig; |
| + | # define loopinfo lconfig.info |
| + | #else |
| bb_loop_info loopinfo; | |
| + | #endif |
| rc = ioctl(lfd, BB_LOOP_GET_STATUS, &loopinfo); | |
| /* If device is free, try to claim it */ | |
| if (rc && errno == ENXIO) { | |
| - | /* Associate free loop device with file */ |
| - | rc = ioctl(lfd, LOOP_SET_FD, ffd); |
| - | if (rc != 0) { |
| - | /* Ouch... race: the device already has a fd */ |
| - | return -1; |
| - | } |
| + | #if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE |
| + | memset(&lconfig, 0, sizeof(lconfig)); |
| + | #else |
| memset(&loopinfo, 0, sizeof(loopinfo)); | |
| + | #endif |
| safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE); | |
| loopinfo.lo_offset = offset; | |
| loopinfo.lo_sizelimit = sizelimit; | |
| @@ -140,6 +153,25 @@ static int set_loopdev_params(int ffd, | |
| * is wrong (would free the loop device!) | |
| */ | |
| loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY); | |
| + | |
| + | #if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE |
| + | lconfig.fd = ffd; |
| + | rc = ioctl(lfd, LOOP_CONFIGURE, &lconfig); |
| + | if (rc == 0) |
| + | return rc; /* SUCCESS! */ |
| + | # if ENABLE_TRY_LOOP_CONFIGURE |
| + | if (errno != EINVAL) |
| + | return rc; /* error other than old kernel */ |
| + | /* Old kernel, fall through into old way to do it: */ |
| + | # endif |
| + | #endif |
| + | #if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_NO_LOOP_CONFIGURE |
| + | /* Associate free loop device with file */ |
| + | rc = ioctl(lfd, LOOP_SET_FD, ffd); |
| + | if (rc != 0) { |
| + | /* Ouch... race: the device already has a fd */ |
| + | return rc; |
| + | } |
| rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo); | |
| if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) { | |
| /* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */ | |
| @@ -151,8 +183,10 @@ static int set_loopdev_params(int ffd, | |
| return rc; /* SUCCESS! */ | |
| /* failure, undo LOOP_SET_FD */ | |
| ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary | |
| + | #endif |
| } | |
| return -1; | |
| + | #undef loopinfo |
| } | |
| /* Returns opened fd to the loop device, <0 on error. | |
| @@ -227,7 +261,7 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse | |
| goto try_next_loopN; | |
| } | |
| - | rc = set_loopdev_params(ffd, lfd, file, offset, sizelimit, flags); |
| + | rc = set_loopdev_params(lfd, ffd, file, offset, sizelimit, flags); |
| if (rc == 0) { | |
| /* SUCCESS! */ | |
| if (!*device) | |