Merging upstream version 1.11.0+dfsg.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 61 insertions, 0 deletions

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+
+# PROCFILE
+
+procfile is a library for reading text data files (i.e `/proc` files) in the fastest possible way.
+
+## How it works
+
+The library automatically adapts (through the iterations) its memory so that each file
+is read with single `read()` call.
+
+Then the library splits the file into words, using the supplied separators.
+The library also supported quoted words (i.e. strings within of which the separators are ignored).
+
+### Initialization
+
+Initially the caller: 
+
+- calls `procfile_open()` to open the file and allocate the structures needed.
+
+### Iterations
+
+For each iteration, the caller:
+
+- calls `procfile_readall()` to read updated contents.
+   This call also rewinds (`lseek()` to 0) before reading it.
+
+   For every file, a [BUFFER](../buffer/) is used that is automatically adjusted to fit
+   the entire file contents of the file. So the file is read with a single `read()` call
+   (providing atomicity / consistency when the data are read from the kernel).
+
+   Once the data are read, 2 arrays of pointers are updated:
+
+   - a `words` array, pointing to each word in the data read
+   - a `lines` array, pointing to the first word for each line
+
+   This is highly optimized. Both arrays are automatically adjusted to
+   fit all contents and are updated in a single pass on the data.
+   
+   The library provides a number of macros:
+   
+   - `procfile_lines()` returns the # of lines read
+   - `procfile_linewords()` returns the # of words in the given line
+   - `procfile_word()` returns a pointer the given word #
+   - `procfile_line()` returns a pointer to the first word of the given line #
+   - `procfile_lineword()` returns a pointer to the given word # of the given line #
+
+### Cleanup
+
+When the caller exits:
+
+- calls `procfile_free()` to close the file and free all memory used.
+
+### Performance
+
+- a **raspberry Pi 1** (the oldest single core one) can process 5.000+ `/proc` files per second.
+- a **J1900 Celeron** processor can process 23.000+ `/proc` files per second per core.
+
+To achieve this kind of performance, the library tries to work in batches so that the code
+and the data are inside the processor's caches.
+
+This library is extensively used in netdata and its plugins.