[syslinux:master] getfssec: update comment explaining next_extent () semantics

[syslinux-bot for H. Peter Anvin]

Commit-ID:  4e8501ccee8f7312a6c33475ece6255050a7ade4
Gitweb:     http://www.syslinux.org/commit/4e8501ccee8f7312a6c33475ece6255050a7ade4
Author:     H. Peter Anvin <hpa at linux.intel.com>
AuthorDate: Wed, 10 Feb 2016 13:47:06 -0800
Committer:  H. Peter Anvin <hpa at linux.intel.com>
CommitDate: Wed, 10 Feb 2016 13:50:18 -0800

getfssec: update comment explaining next_extent() semantics

Update comments which explains next_extent() semantics to be slightly
clearer, and also correct the statement that next_extent can be NULL.

Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>

---
 core/fs/getfssec.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/core/fs/getfssec.c b/core/fs/getfssec.c
index e099b64..2ea122d 100644
--- a/core/fs/getfssec.c
+++ b/core/fs/getfssec.c
@@ -39,18 +39,23 @@
  * will store the initial sector number into inode->next_extent.lstart
  * on return.)
  *
+ * If inode->next_extent.pstart is EXTENT_ZERO, then no disk I/O is
+ * performed, and the data in the extent is all zero.
+ *
  * If inode->next_extent.len != 0 on entry then the routine is allowed
  * to assume inode->next_extent contains valid data from the previous
  * usage, which can be used for optimization purposes.
  *
  * If the filesystem can map the entire file as a single extent
  * (e.g. iso9660), then the filesystem can simply insert the extent
- * information into inode->next_extent at searchdir/iget time, and leave
- * next_extent() as NULL.
+ * information into inode->next_extent at searchdir/iget time, and point
+ * next_extent() to the generic function no_next_extent().
  *
  * Note: the filesystem driver is not required to do extent coalescing,
  * if that is difficult to do; this routine will perform extent lookahead
- * and coalescing.
+ * and coalescing.  However, if the filesystem can do extent coalescing
+ * very cheaply by using filesystem-specific knowledge, then that is
+ * preferred (e.g. FAT).
  */
 
 #include <dprintf.h>