Re: [Libguestfs] [PATCH libnbd 2/2] copy: Fix sparsifying if start is not aligned

When using --sparse=, we may have a case when command start is not aligned to sparse_size and command length is smaller than sparse_size. In this case we advance i after the end of the command, and abort when we try to write after end. To reproduce this issue (with temporary debug logs): $ ./nbdcopy --sparse=$((64*1024)) --threads=1 --requests=1 nbd+unix:///?socket=/tmp/src.sock null: sparsifying range start=0 end=4096 len=4096 write unaligned tail offset=0 end=4096 len=4096 sparsifying range start=1048576 end=1114112 len=65536 write last data start=1048576 end=1114112 len=65536 sparsifying range start=2097152 end=2121728 len=24576 write unaligned tail offset=2097152 end=2121728 len=24576 sparsifying range start=2138112 end=2146304 len=8192 write last data start=2138112 end=2162688 len=24576 lt-nbdcopy: multi-thread-copying.c:351: copy_subcommand: Assertion `offset + len <= end' failed. Aborted (core dumped) Fixed by clipping initial value of i to end of the image. --- copy/multi-thread-copying.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/copy/multi-thread-copying.c b/copy/multi-thread-copying.c index a1f4b19..ac917e9 100644 --- a/copy/multi-thread-copying.c +++ b/copy/multi-thread-copying.c @@ -367,6 +367,12 @@ copy_subcommand (struct command *command, uint64_t offset, size_t len, return newcommand; } +static inline uint64_t +min(uint64_t a, uint64_t b) +{ + return a < b ? a : b; +} + /* Callback called when src has finished one read command. This * initiates a write. */ @@ -399,7 +405,7 @@ finished_read (void *vp, int *error) /* Iterate over whole blocks in the command, starting on a block * boundary. */ - for (i = ROUND_UP (start, sparse_size); + for (i = min (ROUND_UP (start, sparse_size), end); i + sparse_size <= end; i += sparse_size) {