On Thu, Apr 7, 2011 at 11:54 PM, mohit verma <mohit89mlnc@gmail.com> wrote:
On Wed, Apr 6, 2011 at 3:08 AM, Greg Freemyer <greg.freemyer@gmail.com> wrote:
On Tue, Apr 5, 2011 at 4:41 PM, mohit verma <mohit89mlnc@gmail.com> wrote:
hi list, how can a utility like **find** command can map an inode number to a filename? i mean if we pass **find -inum inode_number / ** , it will show us the files associated with that "inode_number". What is the underlying mechanism used in all this ? I have peeped into the findutils code but it seems horrible to figure it out from that code .:)
strace is a lot easier than reading code for something like that.
Looks to me like find is just walking the tree and calling newfstatat() on every file.
Here's a short section from strace. Notice in the directory walk it gets to charmaps. (I think that's /usr/share/i18n/charmaps).
I'd guess that based on the return from newfstatat() it decides its a directory, so it call getdents64()
It then starts calling newfstatat() for everything in that directory. (Not as sexy as you hoped I suspect.)
newfstatat(AT_FDCWD, "charmaps", {st_mode=S_IFDIR|0755, st_size=12288, ...}, AT_SYMLINK_NOFOLLOW) = 0 open("charmaps", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 4 getdents64(4, /* 229 entries */, 32768) = 8024 getdents64(4, /* 0 entries */, 32768) = 0 close(4) = 0 open("charmaps", O_RDONLY|O_NOFOLLOW) = 4 fchdir(4) = 0 close(4) = 0 stat(".", {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0 newfstatat(AT_FDCWD, "CP1257.gz", {st_mode=S_IFREG|0644, st_size=2813, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "EBCDIC-UK.gz", {st_mode=S_IFREG|0644, st_size=2129, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "LATIN-GREEK.gz", {st_mode=S_IFREG|0644, st_size=1605, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "NEXTSTEP.gz", {st_mode=S_IFREG|0644, st_size=2972, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "IBM903.gz", {st_mode=S_IFREG|0644, st_size=1566, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "BIG5-HKSCS.gz", {st_mode=S_IFREG|0644, st_size=145960, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "BRF.gz", {st_mode=S_IFREG|0644, st_size=1166, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "ISO-8859-9E.gz", {st_mode=S_IFREG|0644, st_size=3023, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "MSZ_7795.3.gz", {st_mode=S_IFREG|0644, st_size=1559, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "HP-ROMAN8.gz", {st_mode=S_IFREG|0644, st_size=3193, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "ISO-8859-7.gz", {st_mode=S_IFREG|0644, st_size=3074, ...}, AT_SYMLINK_NOFOLLOW) = 0 newfstatat(AT_FDCWD, "DEC-MCS.gz", {st_mode=S_IFREG|0644, st_size=2948, ...}, AT_SYMLINK_NOFOLLOW) = 0
Hi , i am using 32 bit intel system with ubuntu10.10. And what i got after strace find is something like this: fstatat64(AT_FDCWD, "hints", {st_mode=S_IFDIR|0755, st_size=4096, ...}, AT_SYMLINK_NOFOLLOW) = 0 open("hints", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 5 fchdir(5) = 0 getdents64(5, /* 5 entries */, 32768) = 192 getdents64(5, /* 0 entries */, 32768) = 0 close(5) = 0 fstatat64(AT_FDCWD, "ttf-droid.hints", {st_mode=S_IFREG|0644, st_size=2819, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "ttf-mscorefonts-installer.hints", {st_mode=S_IFREG|0644, st_size=24745, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "ttf-unfonts-core.hints", {st_mode=S_IFREG|0644, st_size=1260, ...}, AT_SYMLINK_NOFOLLOW) = 0 open("..", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_NOFOLLOW) = 5 fstat64(5, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 fchdir(5) = 0 close(5) = 0 fstatat64(AT_FDCWD, "ps-cset-enc.data", {st_mode=S_IFREG|0644, st_size=3983, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "loc-cset.data", {st_mode=S_IFREG|0644, st_size=1261, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "fontconfig.subst-rule", {st_mode=S_IFREG|0644, st_size=1015, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "xenc-cset.data", {st_mode=S_IFREG|0644, st_size=530, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "csetenc-xenc.data2", {st_mode=S_IFREG|0644, st_size=580, ...}, AT_SYMLINK_NOFOLLOW) = 0 open("..", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_NOFOLLOW) = 5 fstat64(5, {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0 fchdir(5) = 0 close(5) = 0 fstatat64(AT_FDCWD, "environment", {st_mode=S_IFREG|0644, st_size=79, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "gnome-vfs-2.0", {st_mode=S_IFDIR|0755, st_size=4096, ...}, AT_SYMLINK_NOFOLLOW) = 0 open("gnome-vfs-2.0", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 5 fchdir(5) = 0 getdents64(5, /* 3 entries */, 32768) = 80 getdents64(5, /* 0 entries */, 32768) = 0 close(5) = 0 fstatat64(AT_FDCWD, "modules", {st_mode=S_IFDIR|0755, st_size=4096, ...}, AT_SYMLINK_NOFOLLOW) = 0 open("modules", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 5 fchdir(5) = 0 getdents64(5, /* 4 entries */, 32768) = 128 getdents64(5, /* 0 entries */, 32768) = 0 close(5) = 0 fstatat64(AT_FDCWD, "extra-modules.conf", {st_mode=S_IFREG|0644, st_size=225, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "default-modules.conf", {st_mode=S_IFREG|0644, st_size=300, ...}, AT_SYMLINK_NOFOLLOW) = 0 open("..", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_NOFOLLOW) = 5 fstat64(5, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 fchdir(5) = 0 close(5) = 0 open("..", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_NOFOLLOW) = 5 fstat64(5, {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0 fchdir(5) = 0 close(5) = 0 fstatat64(AT_FDCWD, "gshadow", {st_mode=S_IFREG|0640, st_size=974, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "manpath.config", {st_mode=S_IFREG|0644, st_size=5173, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brltty", {st_mode=S_IFDIR|0755, st_size=12288, ...}, AT_SYMLINK_NOFOLLOW) = 0 open("brltty", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 5 fchdir(5) = 0 getdents64(5, /* 265 entries */, 32768) = 9720 brk(0x975a000) = 0x975a000 getdents64(5, /* 0 entries */, 32768) = 0 close(5) = 0 fstatat64(AT_FDCWD, "kbd-keypad.ktb", {st_mode=S_IFREG|0644, st_size=2944, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "letters-latin-dot8.tti", {st_mode=S_IFREG|0644, st_size=3793, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brltty-vr-all.hlp", {st_mode=S_IFREG|0644, st_size=69, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "mt.ttb", {st_mode=S_IFREG|0644, st_size=2203, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-front9.kti", {st_mode=S_IFREG|0644, st_size=1777, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-status4.kti", {st_mode=S_IFREG|0644, st_size=1160, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "kbd-braille.kti", {st_mode=S_IFREG|0644, st_size=1913, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "sv.ttb", {st_mode=S_IFREG|0644, st_size=838, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "gujarati.tti", {st_mode=S_IFREG|0644, st_size=5279, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "tamil.tti", {st_mode=S_IFREG|0644, st_size=4356, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brltty-ec-all.hlp", {st_mode=S_IFREG|0644, st_size=866, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "sw.ttb", {st_mode=S_IFREG|0644, st_size=1262, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-bm-display6.kti", {st_mode=S_IFREG|0644, st_size=2887, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-elba_trio_20.ktb", {st_mode=S_IFREG|0644, st_size=872, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "sa.ttb", {st_mode=S_IFREG|0644, st_size=886, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-el80_ii.ktb", {st_mode=S_IFREG|0644, st_size=865, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-routing.kti", {st_mode=S_IFREG|0644, st_size=969, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "fr-2007.ttb", {st_mode=S_IFREG|0644, st_size=12529, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "ny.ctb", {st_mode=S_IFREG|0644, st_size=1269, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "fr-cbifs.ttb", {st_mode=S_IFREG|0644, st_size=11267, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "en_CA.ttb", {st_mode=S_IFREG|0644, st_size=6653, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brltty-ts-pb40.hlp", {st_mode=S_IFREG|0644, st_size=3313, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-al-abt_small.ktb", {st_mode=S_IFREG|0644, st_size=880, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-hm-sync.ktb", {st_mode=S_IFREG|0644, st_size=1679, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "bengali.tti", {st_mode=S_IFREG|0644, st_size=4857, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-ht-bs80.ktb", {st_mode=S_IFREG|0644, st_size=868, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "bo.ttb", {st_mode=S_IFREG|0644, st_size=4629, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "fr_CA.ttb", {st_mode=S_IFREG|0644, st_size=11512, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "sat.ttb", {st_mode=S_IFREG|0644, st_size=923, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "te.ttb", {st_mode=S_IFREG|0644, st_size=880, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-bar.kti", {st_mode=S_IFREG|0644, st_size=1189, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brltty-mn-all.hlp", {st_mode=S_IFREG|0644, st_size=2074, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "dra.ttb", {st_mode=S_IFREG|0644, st_size=882, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-sk-all.ktb", {st_mode=S_IFREG|0644, st_size=2698, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "ja.ctb", {st_mode=S_IFREG|0644, st_size=8450, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-elba_trio_32.ktb", {st_mode=S_IFREG|0644, st_size=872, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "letters-latin.tti", {st_mode=S_IFREG|0644, st_size=3752, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "fr.ttb", {st_mode=S_IFREG|0644, st_size=837, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-bm-display7.kti", {st_mode=S_IFREG|0644, st_size=2215, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "fr-integral.ctb", {st_mode=S_IFREG|0644, st_size=3843, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "pl.ttb", {st_mode=S_IFREG|0644, st_size=11576, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "sd.ttb", {st_mode=S_IFREG|0644, st_size=884, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "de.ttb", {st_mode=S_IFREG|0644, st_size=11217, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "kha.ttb", {st_mode=S_IFREG|0644, st_size=880, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-ht-me88.ktb", {st_mode=S_IFREG|0644, st_size=873, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "de-vollschrift.ctb", {st_mode=S_IFREG|0644, st_size=3289, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "zu.ctb", {st_mode=S_IFREG|0644, st_size=1233, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "gd.ttb", {st_mode=S_IFREG|0644, st_size=3435, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "numbers-nemeth.tti", {st_mode=S_IFREG|0644, st_size=1486, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-bm-vertical.kti", {st_mode=S_IFREG|0644, st_size=916, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-al-abt_large.ktb", {st_mode=S_IFREG|0644, st_size=926, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-status20.kti", {st_mode=S_IFREG|0644, st_size=2610, ...}, AT_SYMLINK_NOFOLLOW) = 0 fstatat64(AT_FDCWD, "brl-pm-status0.kti", {st_mode=S_IFREG|0644, st_size=862, ...}, AT_SYMLINK_NOFOLLOW) = 0
My system doesn't have a system call like newfstatat(). But i suspect (looking at the strace output) that from the starting search directory find opens the dirent stream and manually check inode number (if option -inum) passed to it using fstatat() .
Hmm...actually I think it shouldn't need to do a if all you are trying to do is to find a file by inode number. It can be done just by using directory entries and doing a match of the name. The only reason I can think of doing a stat is to check if some entry is of directory type so that it can descend down. but then I tried "strace find . -maxdepth 1 -inum 5" to limit the descend only to current directory, but unfortunately find still calls stat :-(, don't know why. -- Thanks - Manish