Add readahead cache to gdb's vFile:pread
This patch almost halves the time it takes to "target remote + run to main" on a higher-latency connection. E.g., I've got a ping time of ~85ms to an x86-64 machine on the gcc compile farm (almost 2000km away from me), and I'm behind a ~16Mbit ADSL. When I connect to a gdbserver debugging itself on that machine and run to main, it takes almost 55 seconds: [palves@gcc76] $ ./gdbserver :9999 ./gdbserver [palves@home] $ ssh -L 9999:localhost:9999 gcc76.fsffrance.org [palves@home] $ time ./gdb -data-directory=data-directory -ex "tar rem :9999" -ex "b main" -ex "c" -ex "set confirm off" -ex "quit" Pristine gdb 7.10.50.20150820-cvs gets us: ... Remote debugging using :9999 Reading symbols from target:/home/palves/gdb/build/gdb/gdbserver/gdbserver...done. Reading symbols from target:/lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done. 0x00007ffff7ddd190 in ?? () from target:/lib64/ld-linux-x86-64.so.2 Breakpoint 1 at 0x41200c: file ../../../src/gdb/gdbserver/server.c, line 3635. Continuing. Breakpoint 1, main (argc=1, argv=0x7fffffffe3d8) at ../../../src/gdb/gdbserver/server.c:3635 3635 ../../../src/gdb/gdbserver/server.c: No such file or directory. /home/palves/gdb/build/gdb/gdbserver/gdbserver: No such file or directory. real 0m54.803s user 0m0.329s sys 0m0.064s While with the readahead cache added by this patch, it drops to: real 0m29.462s user 0m0.454s sys 0m0.054s I added a few counters to show cache hit/miss, and got: readahead cache miss 142 readahead cache hit 310 Tested on x86_64 Fedora 20. gdb/ChangeLog: 2015-08-21 Pedro Alves <palves@redhat.com> * remote.c (struct readahead_cache): New. (struct remote_state) <readahead_cache>: New field. (remote_open_1): Invalidate the cache. (readahead_cache_invalidate, readahead_cache_invalidate_fd): New functions. (remote_hostio_pwrite): Invalidate the readahead cache. (remote_hostio_pread): Rename to ... (remote_hostio_pread_vFile): ... this. (remote_hostio_pread_from_cache): New function. (remote_hostio_pread): Reimplement. (remote_hostio_close): Invalidate the readahead cache.
This commit is contained in:
Pedro Alves
parent
88fc5eb7e2
commit
80152258b9
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@ -1,3 +1,17 @@
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2015-08-21 Pedro Alves <palves@redhat.com>
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* remote.c (struct readahead_cache): New.
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(struct remote_state) <readahead_cache>: New field.
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(remote_open_1): Invalidate the cache.
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(readahead_cache_invalidate, readahead_cache_invalidate_fd): New
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functions.
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(remote_hostio_pwrite): Invalidate the readahead cache.
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(remote_hostio_pread): Rename to ...
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(remote_hostio_pread_vFile): ... this.
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(remote_hostio_pread_from_cache): New function.
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(remote_hostio_pread): Reimplement.
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(remote_hostio_close): Invalidate the readahead cache.
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2015-08-21 Marcin Cieślak <saper@saper.info> (tiny patch)
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PR build/18843
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139
gdb/remote.c
139
gdb/remote.c
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@ -228,6 +228,8 @@ static void remote_btrace_reset (void);
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static int stop_reply_queue_length (void);
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static void readahead_cache_invalidate (void);
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/* For "remote". */
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static struct cmd_list_element *remote_cmdlist;
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@ -264,6 +266,29 @@ typedef unsigned char threadref[OPAQUETHREADBYTES];
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#define MAXTHREADLISTRESULTS 32
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/* Data for the vFile:pread readahead cache. */
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struct readahead_cache
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{
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/* The file descriptor for the file that is being cached. -1 if the
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cache is invalid. */
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int fd;
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/* The offset into the file that the cache buffer corresponds
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to. */
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ULONGEST offset;
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/* The buffer holding the cache contents. */
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gdb_byte *buf;
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/* The buffer's size. We try to read as much as fits into a packet
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at a time. */
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size_t bufsize;
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/* Cache hit and miss counters. */
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ULONGEST hit_count;
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ULONGEST miss_count;
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};
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/* Description of the remote protocol state for the currently
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connected target. This is per-target state, and independent of the
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selected architecture. */
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@ -383,6 +408,14 @@ struct remote_state
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Initialized to -1 to indicate that no "vFile:setfs:" packet
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has yet been sent. */
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int fs_pid;
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/* A readahead cache for vFile:pread. Often, reading a binary
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involves a sequence of small reads. E.g., when parsing an ELF
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file. A readahead cache helps mostly the case of remote
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debugging on a connection with higher latency, due to the
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request/reply nature of the RSP. We only cache data for a single
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file descriptor at a time. */
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struct readahead_cache readahead_cache;
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};
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/* Private data that we'll store in (struct thread_info)->private. */
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@ -4561,6 +4594,8 @@ remote_open_1 (const char *name, int from_tty,
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rs->use_threadinfo_query = 1;
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rs->use_threadextra_query = 1;
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readahead_cache_invalidate ();
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if (target_async_permitted)
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{
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/* With this target we start out by owning the terminal. */
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@ -10400,6 +10435,27 @@ remote_hostio_send_command (int command_bytes, int which_packet,
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return ret;
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}
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/* Invalidate the readahead cache. */
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static void
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readahead_cache_invalidate (void)
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{
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struct remote_state *rs = get_remote_state ();
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rs->readahead_cache.fd = -1;
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}
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/* Invalidate the readahead cache if it is holding data for FD. */
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static void
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readahead_cache_invalidate_fd (int fd)
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{
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struct remote_state *rs = get_remote_state ();
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if (rs->readahead_cache.fd == fd)
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rs->readahead_cache.fd = -1;
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}
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/* Set the filesystem remote_hostio functions that take FILENAME
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arguments will use. Return 0 on success, or -1 if an error
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occurs (and set *REMOTE_ERRNO). */
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@ -10478,6 +10534,8 @@ remote_hostio_pwrite (struct target_ops *self,
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int left = get_remote_packet_size ();
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int out_len;
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readahead_cache_invalidate_fd (fd);
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remote_buffer_add_string (&p, &left, "vFile:pwrite:");
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remote_buffer_add_int (&p, &left, fd);
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@ -10493,12 +10551,13 @@ remote_hostio_pwrite (struct target_ops *self,
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remote_errno, NULL, NULL);
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}
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/* Implementation of to_fileio_pread. */
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/* Helper for the implementation of to_fileio_pread. Read the file
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from the remote side with vFile:pread. */
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static int
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remote_hostio_pread (struct target_ops *self,
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int fd, gdb_byte *read_buf, int len,
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ULONGEST offset, int *remote_errno)
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remote_hostio_pread_vFile (struct target_ops *self,
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int fd, gdb_byte *read_buf, int len,
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ULONGEST offset, int *remote_errno)
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{
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struct remote_state *rs = get_remote_state ();
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char *p = rs->buf;
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@ -10532,6 +10591,76 @@ remote_hostio_pread (struct target_ops *self,
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return ret;
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}
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/* Serve pread from the readahead cache. Returns number of bytes
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read, or 0 if the request can't be served from the cache. */
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static int
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remote_hostio_pread_from_cache (struct remote_state *rs,
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int fd, gdb_byte *read_buf, size_t len,
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ULONGEST offset)
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{
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struct readahead_cache *cache = &rs->readahead_cache;
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if (cache->fd == fd
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&& cache->offset <= offset
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&& offset < cache->offset + cache->bufsize)
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{
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ULONGEST max = cache->offset + cache->bufsize;
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if (offset + len > max)
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len = max - offset;
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memcpy (read_buf, cache->buf + offset - cache->offset, len);
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return len;
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}
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return 0;
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}
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/* Implementation of to_fileio_pread. */
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static int
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remote_hostio_pread (struct target_ops *self,
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int fd, gdb_byte *read_buf, int len,
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ULONGEST offset, int *remote_errno)
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{
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int ret;
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struct remote_state *rs = get_remote_state ();
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struct readahead_cache *cache = &rs->readahead_cache;
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ret = remote_hostio_pread_from_cache (rs, fd, read_buf, len, offset);
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if (ret > 0)
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{
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cache->hit_count++;
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if (remote_debug)
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fprintf_unfiltered (gdb_stdlog, "readahead cache hit %s\n",
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pulongest (cache->hit_count));
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return ret;
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}
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cache->miss_count++;
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if (remote_debug)
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fprintf_unfiltered (gdb_stdlog, "readahead cache miss %s\n",
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pulongest (cache->miss_count));
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cache->fd = fd;
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cache->offset = offset;
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cache->bufsize = get_remote_packet_size ();
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cache->buf = xrealloc (cache->buf, cache->bufsize);
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ret = remote_hostio_pread_vFile (self, cache->fd, cache->buf, cache->bufsize,
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cache->offset, remote_errno);
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if (ret <= 0)
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{
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readahead_cache_invalidate_fd (fd);
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return ret;
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}
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cache->bufsize = ret;
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return remote_hostio_pread_from_cache (rs, fd, read_buf, len, offset);
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}
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/* Implementation of to_fileio_close. */
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static int
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@ -10541,6 +10670,8 @@ remote_hostio_close (struct target_ops *self, int fd, int *remote_errno)
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char *p = rs->buf;
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int left = get_remote_packet_size () - 1;
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readahead_cache_invalidate_fd (fd);
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remote_buffer_add_string (&p, &left, "vFile:close:");
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remote_buffer_add_int (&p, &left, fd);
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