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authorPádraig Brady <P@draigBrady.com>2009-12-14 22:45:34 +0000
committerPádraig Brady <P@draigBrady.com>2009-12-25 00:56:41 +0000
commit8d2ecd4a3e30be880b2937bc1d76297a1c2e387a (patch)
treec5eab862b21df8caf952c33a7f3da45954b021a6 /src
parent11dc0016bb72372bbd46b964fb57f4d10448225a (diff)
downloadcoreutils-8d2ecd4a3e30be880b2937bc1d76297a1c2e387a.tar.xz
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.
Diffstat (limited to 'src')
-rw-r--r--src/tail.c130
1 files changed, 116 insertions, 14 deletions
diff --git a/src/tail.c b/src/tail.c
index 71f8a32d1..025680445 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -52,6 +52,12 @@
# include <sys/inotify.h>
/* `select' is used by tail_forever_inotify. */
# include <sys/select.h>
+
+/* inotify needs to know if a file is local. */
+# include "fs.h"
+# if HAVE_SYS_STATFS_H
+# include <sys/statfs.h>
+# endif
#endif
/* The official name of this program (e.g., no `g' prefix). */
@@ -143,6 +149,9 @@ struct File_spec
/* Offset in NAME of the basename part. */
size_t basename_start;
+
+ /* inotify doesn't work for remotely updated files. */
+ bool remote;
#endif
};
@@ -151,6 +160,8 @@ struct File_spec
directories. */
const uint32_t inotify_wd_mask = (IN_MODIFY | IN_ATTRIB | IN_DELETE_SELF
| IN_MOVE_SELF);
+
+static bool fremote (int fd, const char *name);
#endif
/* Keep trying to open a file even if it is inaccessible when tail starts
@@ -201,8 +212,7 @@ static bool have_read_stdin;
more expensive) code unconditionally. Intended solely for testing. */
static bool presume_input_pipe;
-/* If nonzero then don't use inotify even if available.
- Intended solely for testing. */
+/* If nonzero then don't use inotify even if available. */
static bool disable_inotify;
/* For long options that have no equivalent short option, use a
@@ -921,6 +931,17 @@ recheck (struct File_spec *f, bool blocking)
quote (pretty_name (f)));
f->ignore = true;
}
+#if HAVE_INOTIFY
+ else if (!disable_inotify && fremote (fd, pretty_name (f)))
+ {
+ ok = false;
+ f->errnum = -1;
+ error (0, 0, _("%s has been replaced with a remote file. "
+ "giving up on this name"), quote (pretty_name (f)));
+ f->ignore = true;
+ f->remote = true;
+ }
+#endif
else
{
f->errnum = 0;
@@ -1153,6 +1174,74 @@ tail_forever (struct File_spec *f, size_t n_files, double sleep_interval)
#if HAVE_INOTIFY
+/* Return true if any of the N_FILES files in F are remote, i.e., have
+ open file descriptors and are on network file systems. */
+
+static bool
+any_remote_files (const struct File_spec *f, size_t n_files)
+{
+ size_t i;
+
+ for (i = 0; i < n_files; i++)
+ if (0 <= f[i].fd && f[i].remote)
+ return true;
+ return false;
+}
+
+/* Return true if any of the N_FILES files in F represent
+ stdin and are tailable. */
+
+static bool
+tailable_stdin (const struct File_spec *f, size_t n_files)
+{
+ size_t i;
+
+ for (i = 0; i < n_files; i++)
+ if (!f[i].ignore && STREQ (f[i].name, "-"))
+ return true;
+ return false;
+}
+
+static bool
+fremote (int fd, const char *name)
+{
+ bool remote = true; /* be conservative (poll by default). */
+
+# if HAVE_FSTATFS && HAVE_STRUCT_STATFS_F_TYPE && defined __linux__
+ struct statfs buf;
+ int err = fstatfs (fd, &buf);
+ if (err != 0)
+ {
+ error (0, errno, _("cannot determine location of %s. "
+ "reverting to polling"), quote (name));
+ }
+ else
+ {
+ switch (buf.f_type)
+ {
+ case S_MAGIC_AFS:
+ case S_MAGIC_CIFS:
+ case S_MAGIC_CODA:
+ case S_MAGIC_FUSEBLK:
+ case S_MAGIC_FUSECTL:
+ case S_MAGIC_GFS:
+ case S_MAGIC_KAFS:
+ case S_MAGIC_LUSTRE:
+ case S_MAGIC_NCP:
+ case S_MAGIC_NFS:
+ case S_MAGIC_NFSD:
+ case S_MAGIC_OCFS2:
+ case S_MAGIC_SMB:
+ break;
+ default:
+ remote = false;
+ }
+ }
+# endif
+
+ return remote;
+}
+
static size_t
wd_hasher (const void *entry, size_t tabsize)
{
@@ -1310,7 +1399,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
struct inotify_event *ev;
/* When watching a PID, ensure that a read from WD will not block
- indefinetely. */
+ indefinitely. */
if (pid)
{
if (writer_is_dead)
@@ -1362,7 +1451,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
ev = (struct inotify_event *) (evbuf + evbuf_off);
evbuf_off += sizeof (*ev) + ev->len;
- if (ev->len)
+ if (ev->len) /* event on ev->name in watched directory */
{
for (i = 0; i < n_files; i++)
{
@@ -1377,6 +1466,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
if (i == n_files)
continue;
+ /* It's fine to add the same file more than once. */
f[i].wd = inotify_add_watch (wd, f[i].name, inotify_wd_mask);
if (f[i].wd < 0)
@@ -1649,6 +1739,9 @@ tail_file (struct File_spec *f, uintmax_t n_units)
to avoid a race condition described by Ken Raeburn:
http://mail.gnu.org/archive/html/bug-textutils/2003-05/msg00007.html */
record_open_fd (f, fd, read_pos, &stats, (is_stdin ? -1 : 1));
+#if HAVE_INOTIFY
+ f->remote = fremote (fd, pretty_name (f));
+#endif
}
}
else
@@ -2012,19 +2105,28 @@ main (int argc, char **argv)
if (forever && ignore_fifo_and_pipe (F, n_files))
{
#if HAVE_INOTIFY
- /* If the user specifies stdin via a command line argument of "-",
- or implicitly by providing no arguments, we won't use inotify.
+ /* tailable_stdin() checks if the user specifies stdin via "-",
+ or implicitly by providing no arguments. If so, we won't use inotify.
Technically, on systems with a working /dev/stdin, we *could*,
but would it be worth it? Verifying that it's a real device
and hooked up to stdin is not trivial, while reverting to
- non-inotify-based tail_forever is easy and portable. */
- bool stdin_cmdline_arg = false;
-
- for (i = 0; i < n_files; i++)
- if (!F[i].ignore && STREQ (F[i].name, "-"))
- stdin_cmdline_arg = true;
-
- if (!disable_inotify && !stdin_cmdline_arg)
+ non-inotify-based tail_forever is easy and portable.
+
+ any_remote_files() checks if the user has specified any
+ files that reside on remote file systems. inotify is not used
+ in this case because it would miss any updates to the file
+ that were not initiated from the local system.
+
+ FIXME: inotify doesn't give any notification when a new
+ (remote) file or directory is mounted on top a watched file.
+ When follow_mode == Follow_name we would ideally like to detect that.
+ Note if there is a change to the original file then we'll
+ recheck it and follow the new file, or ignore it if the
+ file has changed to being remote. */
+ if (tailable_stdin (F, n_files) || any_remote_files (F, n_files))
+ disable_inotify = true;
+
+ if (!disable_inotify)
{
int wd = inotify_init ();
if (wd < 0)