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tail: fix --follow to not use inotify on remote files
* src/tail.c (struct File_spec): Add a flag to record if file is remote. (recheck): If we're using inotify then check if the file has gone remote and if so, drop it with a warning. (any_remote_files): A new function to check for any open remote files. (tailable_stdin): A new function to refactor the check for whether a tailable file was specified through stdin. (fremote): A new function to check if a file descriptor refers to a remote file. (tail_forever_inotify): Add some comments. (tail_file): Record if a file is remote when initially opened. (main): Disable inotify if any remote files specified. Also document the caveat about remounted files not being noticed by inotify. * NEWS: Mention the fix.
This commit is contained in:
Pádraig Brady
parent
11dc0016bb
commit
8d2ecd4a3e
5
NEWS
5
NEWS
@ -13,6 +13,11 @@ GNU coreutils NEWS -*- outline -*-
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and rpc_pipefs. Also Minix V3 is displayed correctly as minix3, not minux3.
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[bug introduced in coreutils-8.1]
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tail -f (inotify-enabled) once again works with remote files.
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The use of inotify with remote files meant that any changes to those
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files that was not done from the local system would go unnoticed.
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[bug introduced in coreutils-7.5]
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touch -a once again guarantees that a file's change time is
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adjusted, working around a bug in current Linux kernels.
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[bug introduced in coreutils-8.1]
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126
src/tail.c
126
src/tail.c
@ -52,6 +52,12 @@
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# include <sys/inotify.h>
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/* `select' is used by tail_forever_inotify. */
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# include <sys/select.h>
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/* inotify needs to know if a file is local. */
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# include "fs.h"
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# if HAVE_SYS_STATFS_H
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# include <sys/statfs.h>
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# endif
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#endif
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/* The official name of this program (e.g., no `g' prefix). */
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@ -143,6 +149,9 @@ struct File_spec
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/* Offset in NAME of the basename part. */
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size_t basename_start;
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/* inotify doesn't work for remotely updated files. */
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bool remote;
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#endif
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};
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@ -151,6 +160,8 @@ struct File_spec
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directories. */
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const uint32_t inotify_wd_mask = (IN_MODIFY | IN_ATTRIB | IN_DELETE_SELF
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| IN_MOVE_SELF);
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static bool fremote (int fd, const char *name);
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#endif
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/* Keep trying to open a file even if it is inaccessible when tail starts
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@ -201,8 +212,7 @@ static bool have_read_stdin;
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more expensive) code unconditionally. Intended solely for testing. */
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static bool presume_input_pipe;
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/* If nonzero then don't use inotify even if available.
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Intended solely for testing. */
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/* If nonzero then don't use inotify even if available. */
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static bool disable_inotify;
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/* For long options that have no equivalent short option, use a
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@ -921,6 +931,17 @@ recheck (struct File_spec *f, bool blocking)
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quote (pretty_name (f)));
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f->ignore = true;
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}
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#if HAVE_INOTIFY
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else if (!disable_inotify && fremote (fd, pretty_name (f)))
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{
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ok = false;
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f->errnum = -1;
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error (0, 0, _("%s has been replaced with a remote file. "
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"giving up on this name"), quote (pretty_name (f)));
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f->ignore = true;
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f->remote = true;
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}
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#endif
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else
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{
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f->errnum = 0;
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@ -1153,6 +1174,74 @@ tail_forever (struct File_spec *f, size_t n_files, double sleep_interval)
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#if HAVE_INOTIFY
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/* Return true if any of the N_FILES files in F are remote, i.e., have
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open file descriptors and are on network file systems. */
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static bool
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any_remote_files (const struct File_spec *f, size_t n_files)
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{
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size_t i;
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for (i = 0; i < n_files; i++)
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if (0 <= f[i].fd && f[i].remote)
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return true;
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return false;
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}
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/* Return true if any of the N_FILES files in F represent
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stdin and are tailable. */
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static bool
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tailable_stdin (const struct File_spec *f, size_t n_files)
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{
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size_t i;
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for (i = 0; i < n_files; i++)
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if (!f[i].ignore && STREQ (f[i].name, "-"))
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return true;
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return false;
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}
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static bool
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fremote (int fd, const char *name)
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{
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bool remote = true; /* be conservative (poll by default). */
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# if HAVE_FSTATFS && HAVE_STRUCT_STATFS_F_TYPE && defined __linux__
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struct statfs buf;
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int err = fstatfs (fd, &buf);
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if (err != 0)
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{
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error (0, errno, _("cannot determine location of %s. "
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"reverting to polling"), quote (name));
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}
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else
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{
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switch (buf.f_type)
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{
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case S_MAGIC_AFS:
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case S_MAGIC_CIFS:
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case S_MAGIC_CODA:
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case S_MAGIC_FUSEBLK:
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case S_MAGIC_FUSECTL:
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case S_MAGIC_GFS:
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case S_MAGIC_KAFS:
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case S_MAGIC_LUSTRE:
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case S_MAGIC_NCP:
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case S_MAGIC_NFS:
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case S_MAGIC_NFSD:
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case S_MAGIC_OCFS2:
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case S_MAGIC_SMB:
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break;
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default:
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remote = false;
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}
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}
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# endif
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return remote;
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}
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static size_t
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wd_hasher (const void *entry, size_t tabsize)
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{
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@ -1310,7 +1399,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
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struct inotify_event *ev;
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/* When watching a PID, ensure that a read from WD will not block
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indefinetely. */
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indefinitely. */
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if (pid)
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{
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if (writer_is_dead)
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@ -1362,7 +1451,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
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ev = (struct inotify_event *) (evbuf + evbuf_off);
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evbuf_off += sizeof (*ev) + ev->len;
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if (ev->len)
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if (ev->len) /* event on ev->name in watched directory */
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{
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for (i = 0; i < n_files; i++)
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{
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@ -1377,6 +1466,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
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if (i == n_files)
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continue;
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/* It's fine to add the same file more than once. */
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f[i].wd = inotify_add_watch (wd, f[i].name, inotify_wd_mask);
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if (f[i].wd < 0)
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@ -1649,6 +1739,9 @@ tail_file (struct File_spec *f, uintmax_t n_units)
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to avoid a race condition described by Ken Raeburn:
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http://mail.gnu.org/archive/html/bug-textutils/2003-05/msg00007.html */
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record_open_fd (f, fd, read_pos, &stats, (is_stdin ? -1 : 1));
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#if HAVE_INOTIFY
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f->remote = fremote (fd, pretty_name (f));
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#endif
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}
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}
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else
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@ -2012,19 +2105,28 @@ main (int argc, char **argv)
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if (forever && ignore_fifo_and_pipe (F, n_files))
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{
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#if HAVE_INOTIFY
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/* If the user specifies stdin via a command line argument of "-",
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or implicitly by providing no arguments, we won't use inotify.
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/* tailable_stdin() checks if the user specifies stdin via "-",
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or implicitly by providing no arguments. If so, we won't use inotify.
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Technically, on systems with a working /dev/stdin, we *could*,
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but would it be worth it? Verifying that it's a real device
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and hooked up to stdin is not trivial, while reverting to
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non-inotify-based tail_forever is easy and portable. */
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bool stdin_cmdline_arg = false;
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non-inotify-based tail_forever is easy and portable.
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for (i = 0; i < n_files; i++)
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if (!F[i].ignore && STREQ (F[i].name, "-"))
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stdin_cmdline_arg = true;
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any_remote_files() checks if the user has specified any
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files that reside on remote file systems. inotify is not used
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in this case because it would miss any updates to the file
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that were not initiated from the local system.
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if (!disable_inotify && !stdin_cmdline_arg)
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FIXME: inotify doesn't give any notification when a new
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(remote) file or directory is mounted on top a watched file.
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When follow_mode == Follow_name we would ideally like to detect that.
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Note if there is a change to the original file then we'll
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recheck it and follow the new file, or ignore it if the
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file has changed to being remote. */
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if (tailable_stdin (F, n_files) || any_remote_files (F, n_files))
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disable_inotify = true;
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if (!disable_inotify)
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{
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int wd = inotify_init ();
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if (wd < 0)
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