[LU-15743] "lfs find" is missing "-xattr" support

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Labels: lad23dd lug23dd medium
• Assignee: Thomas Bertschinger
• Reporter: Andreas Dilger

Description

It would be useful if "lfs find" could check/match xattrs on files.

This should use "--xattr <name>" to match files that have a <name> xattr, and "--xattr-match <name>=<value>", where <name> and <value> are shell patterns that can match arbitrary text strings in the xattr. The output would be printed in plain text with escaped control characters.

Issue Links

• is related to: LU-17219 lfs find: add ability to print extended attributes
• is related to: LU-18889 "lfs find -printf" optimization
• is related to: LU-15837 "lfs find -printf" improvements
• is related to: LU-16760 "lfs find" support for fscrypt and other file attributes
• is related to: LU-5170 lfs usability
• is related to: LU-13031 store JobID of program that created file in inodes at create time
• is related to: LU-16798 lfs find: new --jobid option

Comments

[Peter Jones]

Landed for 2.16

[Gerrit Updater]

"Oleg Drokin <[e-mail]>" merged in patch https://review.whamcloud.com/c/fs/lustre-release/+/52804/
Subject: LU-15743 utils: add --xattr option to lfs find
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 978ff35d39e3f640a2bfc766b97982012ce07a80

[Andreas Dilger]

I had suggested to use regex_comp(..., REG_NOSUB), but I think the pmatch option is best. I think it is non-intuitive to make the user specify '^' or '$' to terminate the regexp.

[Thomas Bertschinger]

Andreas, adding a question here instead of on the Gerrit review about the regex matching issue, since it's more of a user interface / design question.

I'm not really thrilled that the regex is implicitly matching only part of the string for both the name and value, rather than explicitly requiring a wildcard for the remainder.  That makes it harder to match names/values that are subsets of each other, like "system.acl" "system.acl_default" or whatever.
I would have assumed that it needs a regex "trusted.*" to explicitly match the name of all "trusted.*" xattrs.  Otherwise, it will be harder to match substrings in the xattr name.  I see that this is how getfattr works for "-m", but conversely "find -regex f" does not return all files with "f" in them (not for any regextype), only when "find -regex '.*f.*'" or "find -path '*f*'" is used does that happen.

It looks like GNU find uses a non-POSIX regex interface from Gnulib, and its matching function re_match returns the number of chars matched. So GNU find accomplishes this with basically

if (re_match(..., path, ...) == strlen(path))
...

It should be possible to achieve the same result with the POSIX regex interface using the pmatch[] argument to regexec, like this:

regmatch_t pmatch[1];

regexec(re, input, 1, pmatch, 0);
if (pmatch[0].rm_so == 0 && pmatch[0].rm_eo == strlen(input)) {
        /* matched entire input string */
}

Alternatively, with the current behavior, matching the entire string could be accomplished by the user with anchors: 

lfs find --xattr "^user.*$ /mnt/lustre

This could be documented/suggested in the man page to make it clear to the user if they want this behavior.

A final option could be to use the Gnulib regex instead of POSIX regex for lfs find, but I'm not sure if that really makes sense.

What do you think is the best option?

[Andreas Dilger]

There is a prototype patch for "GNU find" at https://gitlab.com/mweetman/findutils that adds "-xattr" support. According to the find.1 man page in that patch, the "-xattr PATTERN" option takes a regular expression for PATTERN by default, but it also allows the "-regextype TYPE" option to change the regular expression type to one of emacs, posix-awk, posix-basic, posix-egrep, and posix-extended. I don't think there is any urgent need for this, since "lfs find" implements neither the "-path" or "-regex" tests.

[Gerrit Updater]

"Thomas Bertschinger <[e-mail]>" uploaded a new patch: https://review.whamcloud.com/c/fs/lustre-release/+/52804
Subject: LU-15743 utils: add --xattr option to lfs find
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: ab05f6780984bf74487cb284ec85bfcf31991d60