libbb: introduce and use nonblock_safe_read(). Yay!

Our shells are immune from this nasty O_NONBLOCK now!

function                                             old     new   delta
nonblock_safe_read                                     -      78     +78
file_get                                             276     295     +19
generateMTFValues                                    428     435      +7
read_line_input                                     1776    1772      -4
preadbuffer                                          543     450     -93
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/2 up/down: 104/-97)             Total: 7 bytes
   text    data     bss     dec     hex filename
 615190     715   23924  639829   9c355 busybox_old
 615168     715   23924  639807   9c33f busybox_unstripped

1 files changed, 2 insertions, 0 deletions

diff --git a/include/libbb.h b/include/libbb.h
index a91eac4..eb8b2f6 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -475,6 +475,7 @@ extern void *xzalloc(size_t size);
 extern void *xrealloc(void *old, size_t size);
 
 extern ssize_t safe_read(int fd, void *buf, size_t count);
+extern ssize_t nonblock_safe_read(int fd, void *buf, size_t count);
 extern ssize_t full_read(int fd, void *buf, size_t count);
 extern void xread(int fd, void *buf, size_t count);
 extern unsigned char xread_char(int fd);
@@ -482,6 +483,7 @@ extern unsigned char xread_char(int fd);
 extern char *reads(int fd, char *buf, size_t count);
 // Read one line a-la fgets. Reads byte-by-byte.
 // Useful when it is important to not read ahead.
+// Bytes are appended to pfx (which must be malloced, or NULL).
 extern char *xmalloc_reads(int fd, char *pfx);
 extern ssize_t read_close(int fd, void *buf, size_t count);
 extern ssize_t open_read_close(const char *filename, void *buf, size_t count);