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4498bd8179
Currently, the volserver SAFSVolDump RPC and the 'voldump' utility
handle short reads from pread() for vnode payloads by padding the
missing data with NUL bytes. That is, if we request 4k of data for our
pread() call, and we only get back 1k of data, we'll write 1k of data
to the volume dump stream followed by 3k of NUL bytes, and log
messages like this:
1 Volser: DumpFile: Error reading inode 1234 for vnode 5678
1 Volser: DumpFile: Null padding file: 3072 bytes at offset 40960
This can happen if we hit EOF on the underlying file sooner than
expected, or if the OS just responds with fewer bytes than requested
for any reason.
The same code path tries to do the same NUL-padding if pread() returns
an error (for example, EIO), padding the entire e.g. 4k block with
NULs. However, in this case, the "padding" code often doesn't work as
intended, because we compare 'n' (set to -1) with 'howMany' (set to 4k
in this example), like so:
if (n < howMany)
Here, 'n' is signed (ssize_t), and 'howMany' is unsigned (size_t), and
so compilers will promote 'n' to the unsigned type, causing this
conditional to fail when n is -1. As a result, all of the relevant log
messages are skipped, and the data in the dumpstream gets corrupted
(we skip a block of data, and our 'howFar' offset goes back by 1). So
this can result in rare silent data corruption in volume dumps, which
can occur during volume releases, moves, etc.
To fix all of this, remove this bizarre NUL-padding behavior in the
volserver. Instead:
- For actual errors from pread(), return an error, like we do for I/O
errors in most other code paths.
- For short reads, just write out the amount of data we actually read,
and keep going.
- For premature EOF, treat it like a pread() error, but log a slightly
different message.
For the 'voldump' utility, the padding behavior can make sense if a
user is trying to recover volume data offline in a disaster recovery
scenario. So for voldump, add a new switch (-pad-errors) to enable the
padding behavior, but change the default behavior to bail out on
errors.
Change-Id: Ibd6e76c5ea0dea95e3354d9b34536296f81b4f67
Reviewed-on: https://gerrit.openafs.org/14255
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
What's in the "doc" subdirectory ** doc/man-pages pod sources for man pages (converted from original IBM html source). ** doc/xml xml sources for manuals (converted from original IBM html source). Note: The doc/xml/AdminRef uses doc/xml/AdminRef/pod2refentry to convert the pod man pages to xml for printing. pod goes directly to html just fine. ** doc/pdf Old Transarc (and possibly pre-Transarc) protocol and API documentation for which we have no other source. ** doc/txt Technical notes, Windows notes, and examples. ** doc/doxygen Configuration files for the doxygen tool to generate documentation from the annotated sources. See the 'dox' Makefile target in the top level Makefile.