Justin Gottula 7138fe7205 Print zvol_id error messages to stderr rather than stdout ... The zvol_id program is invoked by udev, via a PROGRAM key in the 60-zvol.rules.in rule file, to determine the "pretty" /dev/zvol/* symlink paths paths that should be generated for each opaquely named /dev/zd* dev node. The udev rule uses the PROGRAM key, followed by a SYMLINK+= assignment containing the %c substitution, to collect the program's stdout and then "paste" it directly into the name of the symlink(s) to be created. Unfortunately, as currently written, zvol_id outputs both its intended output (a single string representing the symlink path that should be created to refer to the name of the dataset whose /dev/zd* path is given) AND its error messages (if any) to stdout. When processing PROGRAM keys (and others, such as IMPORT{program}), udev uses only the data written to stdout for functional purposes. Any data written to stderr is used solely for the purposes of logging (if udev's log_level is set to debug). The unintended consequence of this is as follows: if zvol_id encounters an error condition; and then udev fails to halt processing of the current rule (either because zvol_id didn't return a nonzero exit status, or because the PROGRAM key in the rule wasn't written properly to result in a "non-match" condition that would stop the current rule on a nonzero exit); then udev will create a space-delimited list of symlink names derived directly from the words of the error message string! I've observed this exact behavior on my own system, in a situation where the open() syscall on /dev/zd* dev nodes was failing sporadically (for reasons that aren't especially relevant here). Because the open() call failed, zvol_id printed "Unable to open device file: /dev/zd736\n" to stdout and then exited. The udev rule finished with SYMLINK+="zvol/%c %c". Assuming a volume name like pool/foo/bar, this would ordinarily expand to SYMLINK+="zvol/pool/foo/bar pool/foo/bar" and would cause symlinks to be created like this: /dev/zvol/pool/foo/bar -> /dev/zd736 /dev/pool/foo/bar -> /dev/zd736 But because of the combination of error messages being printed to stdout, and the udev syntax freely accepting a space-delimited sequence of names in this context, the error message string "Unable to open device file: /dev/zd736\n" in reality expanded to SYMLINK+="zvol/Unable to open device file: /dev/zd736" which caused the following symlinks to actually be created: /dev/zvol/Unable -> /dev/zd736 /dev/to -> /dev/zd736 /dev/open -> /dev/zd736 /dev/device -> /dev/zd736 /dev/file: -> /dev/zd736 /dev//dev/zd736 -> /dev/zd736 (And, because multiple zvols had open() syscall errors, multiple zvols attempted to claim several of those symlink names, resulting in numerous udev errors and timeouts and general chaos.) This commit rectifies all this silliness by simply printing error messages to stderr, as Dennis Ritchie originally intended. 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 12:23:38 -07:00
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.gitignore	Added .gitignore for mount.zfs and zvol_id	2011-04-07 10:28:38 -07:00
Makefile.am	cppcheck: integrete cppcheck	2021-01-26 16:12:26 -08:00
zvol_id_main.c	Print zvol_id error messages to stderr rather than stdout	2021-09-14 12:23:38 -07:00