It's not the bundle that's opened by fuse, that's just our internal
pointer back to where the data lives. As far as fuse is concerned
the only file we have is sparsebundle.dmg, and that's the file that's
opened and released.
Instead of referencing SB_DATA all over the place, and hence also
calling fuse_get_context(), we now do it once of each function call,
through the renamed sparsebundle_current() macro.
This makes the code a bit more transparent and easier on the eye,
versus the more opaque 'data' type.
sparsebundlefs.cpp:171:56: error: 'pread' was not declared in this scope
sparsebundlefs.cpp:172:24: error: 'close' was not declared in this scope
We were missing unistd.h
FUSE 2.9 added support for zero copy reads/writes through two new
callbacks, read_buf and write_buf. We now imeplement read_buf,
which iterates over the bands using the generic code, but instead
of opening and reading the content of the band into memory, we just
open the file and pass a structure back to FUSE with the file
descriptor, size, and offset, and FUSE will then use this on the
kernel side if possible (using splice on GNU/Linux).
For padding with zeroes we open /dev/zero and treat it as any
other file.
Since FUSE does not provide a callback when it's done with the
buffers there's no way for us to know when to close the bands
we opened. To work around this we keep the files open until
either the main image (dmg) file has been closed, or we run
out of file descriptors, at which point we gc the open files
and continue.
If a read was requested at an offset just before the end of a band,
with a length sufficiently large to cross over to the next band, we
would pad the remaining space after the initial band with zeroes,
and never proceed to read the second band.
We now limit the size of each consecutive band read to the end of the
band, so that the while loop will correctly continue with the next
band if there's still more data to be read.
Adds some sanity checking of the 'size' and 'band-size' values from the
Info.plist file, and ensures they are within the range of off_t, which
happens to be 64 bit due to FUSE forcing the use of _FILE_OFFSET_BITS=64.
