To save more space (equivalent to the size of one erase sector of
MTD device) and to achieve faster read and write speeds, a method
for direct writing was introduced at the FTL layer.
This can be accomplished simply by using the following oflags during
the open operation:
1. O_DIRECT. when this flag is passed in, ftl internally uses
the direct write strategy and no read cache is used in ftl;
otherwise, each write will be executed with the minimum
granularity of flash erase sector size which means a
"sector read back - erase sector - write sector" operation
is performed by using a read cache buffer in heap.
2. O_SYNC. When this flag is passed in, we assume that the
flash has been erased in advance and no erasure operation
will be performed internally within ftl. O_SYNC will take
effect only when both O_DIRECT and O_SYNC are passed in
simultaneously.
3. For uniformity, we remapped the mount flag in mount.h and
unified it with the open flag in fcntl.h. The repetitive
parts of their definitions were reused, and the remaining
part of the mount flag redefine to the unused bit of open
flags.
Signed-off-by: jingfei <jingfei@xiaomi.com>
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