/* losetup.c - Loopback setup * * Copyright 2012 Rob Landley <rob@landley.net> * * No standard. (Sigh.) USE_LOSETUP(NEWTOY(losetup, ">2S(sizelimit)#s(show)ro#j:fdca[!afj]", TOYFLAG_SBIN)) config LOSETUP bool "losetup" default y help usage: losetup [-cdrs] [-o OFFSET] [-S SIZE] {-d DEVICE...|-j FILE|-af|{DEVICE FILE}} Associate a loopback device with a file, or show current file (if any) associated with a loop device. Instead of a device: -a Iterate through all loopback devices -f Find first unused loop device (may create one) -j Iterate through all loopback devices associated with FILE existing: -c Check capacity (file size changed) -d Detach loopback device new: -s Show device name (alias --show) -o Start assocation at OFFSET into FILE -r Read only -S Limit SIZE of loopback association (alias --sizelimit) */ #define FOR_losetup #include "toys.h" #include <linux/loop.h> GLOBALS( char *jfile; long offset; long size; int openflags; dev_t jdev; ino_t jino; ) /* todo: basic /dev file association associate DEV FILE #-a cdfjosS allocate new loop device: /dev/loop-control https://lkml.org/lkml/2011/7/26/148 */ // -f: *device is NULL // Perform requested operation on one device. Returns 1 if handled, 0 if error static void loopback_setup(char *device, char *file) { struct loop_info64 *loop = (void *)(toybuf+32); int lfd = -1, ffd = ffd; unsigned flags = toys.optflags; // Open file (ffd) and loop device (lfd) if (file) ffd = xopen(file, TT.openflags); if (!device) { int i, cfd = open("/dev/loop-control", O_RDWR); // We assume /dev is devtmpfs so device creation has no lag. Otherwise // just preallocate loop devices and stay within them. // mount -o loop depends on found device being at the start of toybuf. if (cfd != -1) { if (0 <= (i = ioctl(cfd, 0x4C82))) // LOOP_CTL_GET_FREE sprintf(device = toybuf, "/dev/loop%d", i); close(cfd); } } if (device) lfd = open(device, TT.openflags); // Stat the loop device to see if there's a current association. memset(loop, 0, sizeof(struct loop_info64)); if (-1 == lfd || ioctl(lfd, LOOP_GET_STATUS64, loop)) { if (errno == ENXIO && (flags & (FLAG_a|FLAG_j))) return; if (errno != ENXIO || !file) { perror_msg("%s", device ? device : "-f"); goto done; } } // Skip -j filtered devices if (TT.jfile && (loop->lo_device != TT.jdev || loop->lo_inode != TT.jino)) goto done; // Check size of file or delete existing association if (flags & (FLAG_c|FLAG_d)) { // The constant is LOOP_SET_CAPACITY if (ioctl(lfd, (flags & FLAG_c) ? 0x4C07 : LOOP_CLR_FD, 0)) { perror_msg("%s", device); goto done; } // Associate file with this device? } else if (file) { char *s = xrealpath(file); if (ioctl(lfd, LOOP_SET_FD, ffd)) perror_exit("%s=%s", device, file); loop->lo_offset = TT.offset; loop->lo_sizelimit = TT.size; strncpy((char *)loop->lo_file_name, s, LO_NAME_SIZE); s[LO_NAME_SIZE-1] = 0; if (ioctl(lfd, LOOP_SET_STATUS64, loop)) perror_exit("%s=%s", device, file); if (flags & FLAG_s) printf("%s", device); free(s); } else if (flags & FLAG_f) printf("%s", device); else { xprintf("%s: [%04llx]:%llu (%s)", device, loop->lo_device, loop->lo_inode, loop->lo_file_name); if (loop->lo_offset) xprintf(", offset %llu", loop->lo_offset); if (loop->lo_sizelimit) xprintf(", sizelimit %llu", loop->lo_sizelimit); xputc('\n'); } done: if (file) close(ffd); if (lfd != -1) close(lfd); } // Perform an action on all currently existing loop devices static int dash_a(struct dirtree *node) { char *s = node->name; // Initial /dev node needs to recurse down one level, then only loop[0-9]* if (*s == '/') return DIRTREE_RECURSE; if (strncmp(s, "loop", 4) || !isdigit(s[4])) return 0; s = dirtree_path(node, 0); loopback_setup(s, 0); free(s); return 0; } void losetup_main(void) { char **s; TT.openflags = (toys.optflags & FLAG_r) ? O_RDONLY : O_RDWR; if (TT.jfile) { struct stat st; xstat(TT.jfile, &st); TT.jdev = st.st_dev; TT.jino = st.st_ino; } // With just device, display current association // -a, -f substitute for device // -j substitute for device // new association: S size o offset rs - need a file // existing association: cd // -f(dc FILE) if (toys.optflags & FLAG_f) { if (toys.optc > 1) perror_exit("max 1 arg"); loopback_setup(NULL, *toys.optargs); } else if (toys.optflags & (FLAG_a|FLAG_j)) { if (toys.optc) error_exit("bad args"); dirtree_read("/dev", dash_a); // Do we need one DEVICE argument? } else { char *file = (toys.optflags & (FLAG_d|FLAG_c)) ? NULL : toys.optargs[1]; if (!toys.optc || (file && toys.optc>1)) { toys.exithelp++; perror_exit("needs 1 arg"); } for (s = toys.optargs; *s; s++) loopback_setup(*s, file); } }