config.c: add git_env_ulong() to parse environment variable

The new function parses an integeral value that fits in unsigned
long in human readable form, i.e. possibly with unit suffix, e.g.
10k = 10240, etc., from an environment variable.  Parsing of
GIT_MMAP_LIMIT and GIT_ALLOC_LIMIT will use it in later patches.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
memory_limit: use git_env_ulong() to parse GIT_ALLOC_LIMIT

GIT_ALLOC_LIMIT limits xmalloc()'s size, which is of type size_t.
Better use git_env_ulong() to parse the environment variable, so
that the postfixes 'k', 'm', and 'g' can be used; and use size_t to
store the limit for consistency.  The change to size_t has no direct
practical impact, because the environment variable is only meant to
be used for our own tests, and we use it to test small sizes.

The cast of size in the call to die() is changed to uintmax_t to
match the format string PRIuMAX.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
mmap_limit: introduce GIT_MMAP_LIMIT to allow testing expected mmap size

In order to test expectations about mmap in a way similar to testing
expectations about malloc with GIT_ALLOC_LIMIT introduced by
d41489a6 (Add more large blob test cases, 2012-03-07), introduce a
new environment variable GIT_MMAP_LIMIT to limit the largest allowed
mmap length.

xmmap() is modified to check the size of the requested region and
fail it if it is beyond the limit.  Together with GIT_ALLOC_LIMIT
tests can now confirm expectations about memory consumption.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
copy_fd(): do not close the input file descriptor

The caller, not this function, opened the file descriptor; it is
selfish for the callee to close it when it is done reading from it.
The caller may want an option to rewind and re-read the contents
after it returns.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
SQUASH??? loop in copy_fd() is write_in_full(), essentially

Suggested by peff.
convert: stream from fd to required clean filter to reduce used address space

The data is streamed to the filter process anyway.  Better avoid mapping
the file if possible.  This is especially useful if a clean filter
reduces the size, for example if it computes a sha1 for binary data,
like git media.  The file size that the previous implementation could
handle was limited by the available address space; large files for
example could not be handled with (32-bit) msysgit.  The new
implementation can filter files of any size as long as the filter output
is small enough.

The new code path is only taken if the filter is required.  The filter
consumes data directly from the fd.  If it fails, the original data is
not immediately available.  The condition can easily be handled as
a fatal error, which is expected for a required filter anyway.

If the filter was not required, the condition would need to be handled
in a different way, like seeking to 0 and reading the data.  But this
would require more restructuring of the code and is probably not worth
it.  The obvious approach of falling back to reading all data would not
help achieving the main purpose of this patch, which is to handle large
files with limited address space.  If reading all data is an option, we
can simply take the old code path right away and mmap the entire file.

The environment variable GIT_MMAP_LIMIT, which has been introduced in
a previous commit is used to test that the expected code path is taken.
A related test that exercises required filters is modified to verify
that the data actually has been modified on its way from the file system
to the object store.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>