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If the initial stat() fails then efile_openfile() will still proceed
to open() the file. If that succeeds and the caller passed a non-NULL
pSize, then it will copy bogus data from the statbuf into *pSize. This
has been observed to cause file:read_file/1 to return truncated file
data with no error indication.
The use case involved a large file system mounted via NFS, with some
directories containing large number of files, and NFS mount options
that allow the NFS client to return EIO if the NFS server does not
respond quickly enough. Depending on the caching state of the client
and server machines, a few stat() calls (fewer than 1 per 10 million)
would take long enough to trigger EIO errors, but subsequent open()
calls would succeed, and read_file/1 would return truncated data. This
sequence of events has been observed via "strace" on beam.smp.
Signed-off-by: Mikael Pettersson <[email protected]>
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If writev return an error (eg ENOSPC) we do not want to abort here
but instead propagate upwards into erlang.
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The sync option adds the POSIX O_SYNC flag to the open system call on
platforms that support the flag or its equivalent, e.g.,
FILE_FLAG_WRITE_THROUGH on Windows. For platforms that don't support it,
file:open/2 returns {error, enotsup} if the sync option is passed in.
The semantics of O_SYNC are platform-specific. For example, not all
platforms guarantee that all file metadata are written to the disk along
with the file data when the flag is in effect. This issue is noted in the
documentation this commit adds for the sync option.
Add a test for the sync option. Note however that the underlying OS
semantics for O_SYNC can't be tested automatically in any practical way, so
the test assumes the OS does the right thing with the flag when
present. For manual verification, dtruss on OS X and strace on Linux were
both run against beam processes to watch calls to open(), and file:open/2
was called in Erlang shells to open files for writing, both with and
without the sync option. Both the dtruss output and the strace output
showed that the O_SYNC flag was present in the open() calls when sync was
specified and was clear when sync was not specified.
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This operation allows pre-allocation of space for files.
It succeeds only on systems that support such operation.
The POSIX standard defines the optional system call
posix_fallocate() to implement this feature. However,
some systems implement more specific functions to
accomplish the same operation.
On Linux, if the more specific function fallocate() is
implemented, it is used instead of posix_fallocate(),
falling back to posix_fallocate() if the fallocate()
call failed (it's only supported for the ext4, ocfs2,
xfs and btrfs file systems at the moment).
On Mac OS X it uses the specific fcntl() operation
F_PREALLOCATE, falling back to posix_fallocate() if
it's available (at the moment Mac OS X doesn't provide
posix_fallocate()).
On any other UNIX system, it uses posix_fallocate() if it's
available. Any other system not providing this system call
or any function to pre-allocate space for files, this operation
always fails with the ENOTSUP POSIX error.
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When using values of sfv_len and sfv_off which are larger than
the file in question, sendfilev can sometimes return -1 and send
data. It seems to be only Oracle SunOS which this happens on.
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Ensure displayed sizes are not negative.
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The return value from efile_sendfile was not consistent
inbetween platforms. The API should now be working as it
was intended.
OTP-9994
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* jz/error-logic-efile_sendfile:
erts: minor fix for unnecessary condition
OTP-9872
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* jz/sendfile_chunk_size:
erts: change SENDFILE_CHUNK_SIZE from signed to unsigned
Conflicts:
erts/emulator/drivers/unix/unix_efile.c
OTP-9872
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* ta/sendfile/OTP-9240:
Do not use async threads on DARWIN
Fix cleanup when sendfile process crashes
Return {error,closed} from sendfile if closed
Do not use SFV_NOWAIT as it does not exist on all solaris
Clarify some code comments
Make solaris use sendfilev
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Both mtime and atime were incorrectly checked for zero
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In "while (retval != -1 && retval == SENDFILE_CHUNK_SIZE)", "retval != -1" is pointless.
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It's reasonable to use UL in SENDFILE_CHUNK_SIZE
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Thanks Tuncer Ayaz
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sendfilev is a richer API which allows us to
do non blocking TCP on solaris. The normal
sendfile API seems to have some issue with
non blocking sockets and the return value of
sendfile.
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First stage in utc-time for prim_file.
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Since the API for headers/trailers seem to be very awkward to
work with when using non-blocking io the feature is dropped
for now. See unix_efile.c for more details.
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Have to figure out how to represent progress in header writing when
using non-blocking, not sure how to do this.
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It is not possible to use the maximum size_t/off_t for the chunks
as that causes sendfile to return einval. 3GB seems to work on all
*nix platforms.
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When there are no async threads sendfile will use the
ready_output select on the socket fd to know when to send
data.
The file_desc will also be put in the sending sendfile_state
which buffers all other commands to that file until the
sendfile is done.
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Move sendfile data to invoke data instead of file_descr.
Remove usage of ready_output when doing a send.
If told to send 0 bytes, file_sendfile now sends the entire file
for linux.
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Move the command handling to outputv in preparation for
header and trailer inclusion in the sendfile api.
Use the standard efile communication functions for sendfile.
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Allow Erlang code to use sendfile() where available by wrapping it as
file:sendfile/4 and file:sendfile/2.
sendfile(2) - Linux man page:
"sendfile() copies data between one file descriptor and another.
Because this copying is done within the kernel, sendfile() is more
efficient than the combination of read(2) and write(2), which would
require transferring data to and from user space."
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A long time ago, the Erlang run-time system could be
build with pre-ANSI/ISO-C (K&R) C compilers, but that is
no longer possible. Remove the remaining uses of the
compatibility macros that made it possible that possible.
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Add an option that atomically tests for the existence of a file and
creates it if the file does not exist, by passing the O_EXCL flag
to open() on Unix and CREATE_NEW flag on Windows. Support for O_EXCL
varies across platforms and filesystems.
{ok, Fd} = file:open("/tmp/foo", [write,exclusive]),
{error, eexist} = file:open("/tmp/foo", [write,exclusive]).
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Useful for informing the Operating System about the access pattern
for a file's data, so that it can adapt the caching strategy to
maximize disk IO performance.
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file:datasync/1 invokes the POSIX system call "int fdatasync(int fd)".
This system call is similar to "fsync" but, unlike fsync, it does not
update the metadata associated with the file (like the access time for
example). It's used by many DBMSs (MySQL and SQLite of example) to
increase disk IO performance, as it avoids disk seeks and disk write
operations compared to fsync.
More details on it at:
http://linux.die.net/man/2/fdatasync
An example, from the MySQL source:
http://bazaar.launchpad.net/~mysql/mysql-server/mysql-5.1-telco-6.1/annotate/head%3A/mysys/my_sync.c#L61
This new function just calls fsync on systems not implementing fdatasync.
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* bg/remove-stray-ose-support:
configure: Remove stray OSE/Delta support
Makefiles: Remove stray OSE/Delta support
kernel tests: Remove stray OSE/Delta support
system tests: Remove stray OSE/Delta support
erl_interface tests: Remove stray OSE/Delta support
epmd: Remove stray OSE/Delta support
epmd: #ifdef out start_epmd() for other platforms than VxWorks
emulator tests: Remove stray OSE/Delta support
emulator: Remove stray OSE/Delta support
emulator: Eliminate #ifdef for sys_tty_reset()
test_server: Remove stray support for OSE/Delta
OTP-8585 bg/remove-stray-ose-support
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