Justin Gottula fd2e4d143d Udev rules: use match (==) rather than assign (=) for PROGRAM ... Assignment syntax (=) can be used for the PROGRAM key. But the PROGRAM key is really a match key, not an assign key. The internal logic used by udev to decide whether a PROGRAM key "matched" or not (which determines whether the remainder of the rule is evaluated) depends on whether the operator was OP_MATCH (==) or OP_NOMATCH (!=). [1] The man page claims that '"=", ":=", and "+=" have the same effect as "=="' for PROGRAM keys. And, after a brief perusal, the udev source code does seem to confirm that operators other than OP_MATCH (==) or OP_NOMATCH (!=) are implicitly converted to OP_MATCH (==). [2] But it's not entirely clear that this is definitely the case: anecdotal testing seems to indicate that when OP_ASSIGN (=) is used, the program's exit status is disregarded and the remainder of the rule is processed regardless of whether it was, in fact, a successful exit. The bottom line here is that, if zvol_id hits some snag and returns a nonzero exit status, then we almost certainly do NOT want to continue on with the rule and use whatever the stdout contents may have been to mindlessly create /dev/zvol/* symlinks. Therefore, let's be extra-sure and use the match (==) operator explicitly, to eliminate any possibility that udev might do the wrong thing, and ensure that a nonzero exit status will definitely short-circuit the rest of the rule, bypassing the SYMLINK+= assignments. [1] udev, file src/udev/udev-rules.c, func udev_rule_apply_token_to_event, switch case TK_M_PROGRAM if r != 0 (nonzero exit status): return token->op == OP_NOMATCH; switch case TK_M_PROGRAM if r == 0 (zero exit status): return token->op == OP_MATCH; func retval 0 => key is considered to have matched func retval 1 => key is considered to have NOT matched [2] udev, file src/udev/udev-rules.c, func parse_token, at func start: bool is_match = IN_SET(op, OP_MATCH, OP_NOMATCH); in else-if case streq(key, "PROGRAM"): if (!is_match) op = OP_MATCH; Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com> Signed-off-by: Justin Gottula <justin@jgottula.com> Closes #12302		2021-09-14 12:23:10 -07:00
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rules.d	Udev rules: use match (==) rather than assign (=) for PROGRAM	2021-09-14 12:23:10 -07:00
Makefile.am	Move udev rules from /etc/udev to /lib/udev	2011-08-08 16:21:10 -07:00