https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=eb4bfe4621ecaa49d0b4e586315286f8e4731046
commit eb4bfe4621ecaa49d0b4e586315286f8e4731046 Author: Corinna Vinschen <[email protected]> Date: Tue Dec 19 18:58:06 2017 +0100 cygwin: block devices: fix file offset after short writes When reading/writing block devices, Cygwin emulates Linux, providing a byte-exact file position, albeit the underlying device drivers don't. Unfortunately this only worked correctly for reading. The raw_write method failed to revalidate the buffer after the read-modify-write cycle in case len is not a multiple of the sector length. This in turn resulted in lseek reporting a wrong file pointer. Also, fix a condition for invalidating the buffer after writing from a remaining read buffer. Signed-off-by: Corinna Vinschen <[email protected]> Diff: --- winsup/cygwin/fhandler_floppy.cc | 12 ++++++++++-- winsup/cygwin/release/2.10.0 | 3 +++ 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/winsup/cygwin/fhandler_floppy.cc b/winsup/cygwin/fhandler_floppy.cc index de9e163..cca00ba 100644 --- a/winsup/cygwin/fhandler_floppy.cc +++ b/winsup/cygwin/fhandler_floppy.cc @@ -566,11 +566,11 @@ fhandler_dev_floppy::raw_write (const void *ptr, size_t len) /* Align pointers, lengths, etc. */ cplen = MIN (cplen, written); devbufstart += cplen; + if (devbufstart >= devbufend) + devbufstart = devbufend = 0; p += cplen; len -= cplen; bytes_written += cplen; - if (len) - devbufstart = devbufend = 0; } /* As long as there's still something left in the input buffer ... */ while (len) @@ -607,6 +607,14 @@ fhandler_dev_floppy::raw_write (const void *ptr, size_t len) p += cplen; len -= cplen; bytes_written += cplen; + /* If we overwrote, revalidate devbuf. It still contains the + content from the above read/modify/write. Revalidating makes + sure lseek reports the correct position. */ + if (cplen < bytes_per_sector) + { + devbufstart = cplen; + devbufend = bytes_per_sector; + } } return bytes_written; } diff --git a/winsup/cygwin/release/2.10.0 b/winsup/cygwin/release/2.10.0 index 3afc4b7..0c6b406 100644 --- a/winsup/cygwin/release/2.10.0 +++ b/winsup/cygwin/release/2.10.0 @@ -31,3 +31,6 @@ Bug Fixes - Remove a call to fflush from ftell{o}, which may result in wrong offsets. Addresses: https://cygwin.com/ml/cygwin/2017-12/msg00151.html + +- Fix file pointer computation after short writes on block devices. + Addresses: https://cygwin.com/ml/cygwin/2017-12/msg00151.html
